The Biology and Aquaculture Potential of Cherax quadricarinatus. Потенциал биологии и аквакультуры Cherax quadricarinatus

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The Biology and Aquaculture Potential of the
Tropical Freshwater Crayfish
Article · January 1990
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The Biology and
Aquaculture Potential of
Cherax quadricarinatus
Clive M. Jones
Queensland Department of Primary Industries
and Fisheries
THE BIOLOGY AND AQUACULTURE POTENTIAL OF CHERAX
QUADRICARINATUS
by
CLIVE M. JONES (B.Sc. Hons. Ph.D.)
Queensland Department of Primary Industries, Fisheries Branch, Research Station, Walkamin
Q, Australia 4872.
Contact Details for Clive Jones: Northern Fisheries Centre, PO Box 5396 Cairns, Q 4872.
email clive.jones@dpi.qld.gov.au
THIS DOCUMENT WAS SUBMITTED TO THE RESERVE BANK OF AUSTRALIA
RURAL CREDITS DEVELOPMENT FUND AS A FINAL REPORT FOR THE PROJECT
"The Assessment of Cherax quadricarinatus as a Candidate for Aquaculture". Project No.
QDPI/8860.
1
ACKNOWLEDGEMENTS
I thank Chris Barlow in particular for initiating this project and for his enthusiastic support
throughout. The Fisheries staff of the Walkamin Research Station have all contributed to the
successful completion of this research, and I express my gratitude to them. Les Rodgers, Dave
Bull, Paul Clayton and Peter Graham deserve special thanks for their assistance. I am grateful
to the other staff of Walkamin Research Station who assisted, particularly with the Field
Days.
The patient assistance provided by the Walkamin Research Station secretary, Diane McIntyre,
was always appreciated.
Special thanks are due to Sue Poole and her team for supervision of post-harvest research and
to Charles Hausman for crayfish illustrations.
Unsung heroes of all research projects are our librarians. I express my sincere thanks to
Donna Holmes and Zena Seliga for their patience and faithfull support.
Continued support and encouragement from the Tropical Freshwater Crayfish Farmers
Association and the crayfish farming Industry in general is gratefully acknowledged.
My sincere appreciation goes also to Sharon for her loyal support and counsel always.
This project was jointly funded by the Commonwealth Reserve Bank Rural Credits
Development Fund and The Queensland Department of Primary Industry's Fisheries Branch.
2
TABLE OF CONTENTS
1
GENERAL INTRODUCTION
1
2
TEMPERATURE EXPERIMENTATION
3
2.1
Introduction:
3
2.2
Materials and Methods:
3
2.3
Results:
5
2.4
Discussion:
8
3
SALINITY EXPERIMENTATION
10
3.1
Introduction:
10
3.2
Materials and Methods:
10
3.3
Results:
12
3.4
Discussion:
13
4
JUVENILE NUTRITION AND HABITAT
17
4.1
Introduction:
17
4.2
Materials and Methods:
18
4.3
Results:
19
4.4
Discussion:
20
5
DEVELOPMENT OF HATCHERY/NURSERY PROCEDURES
24
5.1
Introduction:
24
5.2
Materials and Methods:
25
5.3
Results:
28
5.4
Discussion:
39
6
GROWOUT TRIALS - SUPPLEMENTAL FEEDS
44
6.1
Introduction:
44
6.2
Materials and Methods:
46
6.3
Results:
48
3
6.4
7
Discussion:
GROWOUT TRIALS - COMMERCIAL PRODUCTION
50
52
7.1
Introduction:
52
7.2
Materials and Methods:
54
7.3
Results:
56
7.4
Discussion:
61
8
POST-HARVEST ASPECTS
68
8.1
Introduction:
68
8.2
Materials and Methods:
68
8.3
Results and Discussion:
71
8.4
Conclusion:
84
9
GENERAL BIOLOGY CHERAX QUADRICARINATUS
86
9.1
Introduction:
86
9.2
Systematics and Distribution:
86
9.3
Anatomy:
87
9.4
Morphometric Relationships:
90
9.5
Life Cycle:
91
9.6
Reproduction:
92
9.7
Growth:
94
9.8
Feeding:
95
9.9
Respiration:
96
9.10
Behaviour:
97
10
AQUACULTURE POTENTIAL
98
11
BIBLIOGRAPHY
4
100
1
GENERAL INTRODUCTION
Aquaculture has been touted as the 'sunrise' industry of Queensland despite the modest
success achieved to date. There has been considerable interest and some development in the
farming of prawns and the prized barramundi. More recently much attention has been focused
on freshwater crayfish.
Despite the lack of significant development of freshwater crayfish farming elsewhere in
Australia, in 1980 a group of enterprising farmers from south-east Queensland introduced the
Western Australian marron (Cherax tenuimanus) which they surmised would perform well
under the warmer and more equable Queensland climate. Some success and expansion of the
industry was achieved until the particularly warm summer of 1986, when the bulk of the
marron died. Even prior to this natural disaster, some farmers were looking for alternative
species, better suited to the sub-tropics. A relatively unknown crayfish from north
Queensland, Cherax quadricarinatus entered the scene and commercial trials in ex-marron
ponds began. It was soon evident that this species had a substantially greater potential.
C. quadricarinatus along with C. tenuimanus (marron), C. destructor (yabbie) and
approximately 10 other Cherax species, belong to the family Parastacidae, a group of
freshwater crayfish entirely restricted to the southern hemisphere (Chapt.2). C.
quadricarinatus inhabits rivers and streams of Queensland, Northern Territory and New
Guinea. Prior to its emergence as an aquaculture candidate, this species had only been
considered in taxonomic studies (Riek, 1951, 1959, 1969). Unlike the yabbie and marron, C.
quadricarinatus did not support any substantial recreational fishery, primarily because of its
remote distribution. Nothing was known of its biology or life habits.
Initially, consideration of C. quadricarinatus's aquaculture potential was based on its
relatively large size and its familiarity to other aquacultured species. Commercial trials soon
indicated more significant potential, and although biological information was generated, it
was observational or anecdotal.
In 1987, Mr.C. Barlow of the Queensland Department of Primary Industry's Walkamin
Research Station recognised the need for a thorough scientific assessment of this species'
aquaculture potential, and submitted an application for Commonwealth Government
assistance. This was granted from the Reserve Bank's Rural Credits Development Fund, and
research began in 1988.
The objectives of this study were:1. to determine water quality, habitat requirements, stocking density and feeding regimes
for optimal survival and growth under controlled laboratory conditions.
2. to develop broodstock husbandry techniques and intensive juvenile rearing
procedures.
3. to evaluate survival and growth and effective production techniques in ponds,
employing optimal conditions defined from experiments.
4. to examine storage, processing and marketing requirements including export potential,
seasonal demand, flavour and presentation preferences.
The research was based at the Walkamin Research Station on the Atherton Tableland, some
1
70km south-west of Cairns in Far North Queensland. Adjacent to the head waters of the
Mitchell River, this location was ideal as C. quadricarinatus was readily available. Facilities
included a laboratory for controlled experimental studies, a hatchery for holding broodstock
and induced spawning, a greenhouse containing 30 large tanks for holding crayfish and used
also as a nursery, and 6 earthern ponds ranging in size from 0.1 to 0.2 hectares. These
facilities enabled trials to be conducted at a semi-commercial level, such that results were
realistically applicable to the industry.
Laboratory studies were necessary to conduct closely controlled experiments. Effect of
temperature on growth, salinity tolerance and juvenile nutrition and habitat requirements were
investigated in the laboratory in replicated aquarium experiments (Chapters 2 through 4).
Conduct of experiments and particularly grow-out trials necessitated large numbers of
juvenile crayfish. Due to the limited number of ponds available, the extensive pond-based
methods of juvenile production currently employed by the industry were not suitable. In
addition, juveniles were required during winter when pond reproduction does not occur.
These were the initial stimuli to the investigations of induced spawning and controlled rearing
of juvenile C. quadricarinatus. However, the processes involved in this production were of
equal importance. Techniques of broodstock collection and handling, induced spawning,
incubation of eggs and rearing of juveniles were developed from an experimental point of
view. This development constitutes the subject of Chapter 5.
Due to the difficulty of simulating pond conditions in tanks, feeding trials were conducted in
an experimental facility established in an earthern pond. This facility permitted use of a
replicated experimental design under normal pond conditions. A feeding trial was conducted
in this facility (Chapt.6).
Production of berried females and juveniles was sufficient to stock three 0.12ha ponds for
grow-out trials. The entire process including pond preparation, stocking, water management,
feeding, predator control, stock assessment and harvesting is described in Chapter 7.
Aspects of the research involving food technology were planned from Walkamin, but carried
out at the Department of Primary Industry's Food Research Laboratories in Brisbane. Ms Sue
Poole, an experience seafood scientist, kindly offered to supervise this work. Chapter 8,
which covers this research, is based directly on her report.
In the process of conducting the research detailed in chapters 2 through 8, a considerable
amount of biological information was generated indirectly. From this, a description of C.
quadricarinatus's general biology was possible, which is presented in Chapter 9.
A brief summary of key biological attributes which contribute to the aquaculture potential of
C. quadricarinatus is presented in Chapter 10.
2
2
2.1
TEMPERATURE EXPERIMENTATION
Introduction:
The relationship between ambient temperature and growth of aquatic poikilothermic
organisms is a well established one (Kinne, 1964, 1960; Paloheimo and Dickie, 1966b; Brett
et al., 1969). Its nature is characteristic for each species such that optimal growth occurs over
a reasonably narrow and fixed range of temperature and is gradually suppressed at both lower
and higher temperatures.
An understanding of an animals response to temperature, particularly in regard to growth, is
perhaps one of the most fundamental requirements for providing suitable culture conditions.
Although temperature also has an important influence on other physiological processes,
particularly reproduction and lethality, the following experimentation was concerned
primarily with defining temperature conditions appropriate to optimal survival and growth.
Of the variable parameters influencing production in aquaculture, water temperature is the one
over which the operator has least control. Consequently, its significance in determining site
suitability for aquaculture is paramount. Definition of survival/growth response to
temperature was considered essential in assessing the aquaculture potential of Cherax
quadricarinatus.
2.2
Materials and Methods:
Ten treatment combinations were used in a 5 X 2 factorial arrangement of treatments in a
randomized block design with 20 crayfish per treatment. The two factors were water
temperature (20, 24, 28, 32 and 34 S0oTC) and crayfish size (small and large juveniles). Two
aquaria were used for each treatment combination.
20 glass aquaria of 80l capacity were filled with bore water and 5mm of fine river sand was
spread across the bottom. Each tank was equipped with a power filter (Fluval 203) capable of
filtering the total tank volume 6x per hour. Filter media were cleaned regularly. Water was
continuously aerated. Crayfish habitat was provided in the form of 3cm wide strips of
fibreglass fly-screen mesh suspended from a polystyrene float.
Air temperature in the experimental facility was maintained at 18S0oTC and water
temperature of each tank elevated to the desired level by submersible electric aquarium
heaters (Supreme Pet 200w). Tanks were insulated on their four longtitudinal faces with
polystyrene to stabilize temperature fluctuations. Water temperature was recorded 4x per day
by temperature probes connected to a datalogger (Datataker DT100F). Temperature statistics
for each tank over the 70 day period of the experiment are presented in Table 2.1. The
photoperiod was maintained at 14L:10D.
Juvenile crayfish were taken from 2000l 'hatchery tanks' to which berried females had been
introduced some two months previously. These crayfish were divided into two size categories
and their individual weights were measured to the nearest 10mg and recorded. Mean sizes of
crayfish used were: small, 0.61g (S.E. 0.02) and large, 1.27g (S.E. 0.06).
20 crayfish from each size category were randomly assigned to each of the five temperatures,
3
and were acclimated to that temperature at 4S0oTC per day. Food included fish flakes,
chopped earthworm and frozen zooplankton, introduced ad libitum each afternoon and excess
food removed each morning. All crayfish were individually weighed at 14 day intervals up to
and including day 70 at which time the experiment was terminated.
Because individual crayfish were not identifiable, growth was expressed as individual weight
at day 70 minus the mean day 1 weight of each tank. Survival was expressed as the proportion
of crayfish alive at day 70. Differences in growth and survival among the 10 treatment
combinations were compared with analysis of variance. While parametric analyses were
appropriate for growth data, a non-parametric test (Kruskal-Wallis 1-way ANOVA) was
required for survival data. Pairwise comparisons of means were made with Duncan's Multiple
Range test.
Desired Temperature °C
Replicate
20
24
28
32
34
1
20.6
19.9-21.5
23.8
23.2-24.0
27.5
27.1-27.9
31.1
29.8-32.1
33.5
32.5-34.2
2
20.9
20.2-21.7
24.0
23.6-24.3
27.4
26.2-28.0
31.7
30.9-33.0
33.5
32.2-35.0
3
21.0
19.8-22.3
24.0
23.5-24.6
28.0
27.2-28.7
31.5
30.9-32.0
33.6
32.1-34.9
4
20.7
19.5-22.2
24.1
23.7-24.4
28.4
27.3-29.2
31.4
29.9-32.2
33.2
30.8-34.7
Table 2.1. Mean (top figure) and range (bottom figures) of temperature (°C) in each
experimental tank over 70 days.
4
2.3
Results:
Both survival and growth of Cherax quadricarinatus were affected by water temperature.
Survival of crayfish was significantly reduced at 34S0oTC (p<0.01), although there was no
difference in survival at the other four temperatures for which mean survival was equal to or
greater than 0.65 after 70 days (Fig. 2.1). There was no significant difference in survival
between size groups at each temperature.
Analysis of variance indicated significant variability of growth between temperatures
(p<0.01), although no such variability was evident between large and small juveniles (Table
2.2). There was no interactive effect on growth between crayfish size and temperature. Due to
the lack of difference between size groups, all data for each temperature were pooled and reanalysed (Table 2.3).
Growth at 28S0oTC was best (Fig. 2.2) although the means comparisons test indicated that
growth at 24S0oTC was not significantly less (p>0.05) (Table 2.4). Growth of crayfish at
32S0oTC was significantly less than that at 28 and 24S0oTC and significantly greater than at
20 and 34S0oTC. Poor growth at 20 and 34S0oTC suggests that these temperatures represent
high and low extremes respectively for good growth in this species. This is clearly evident in
Figure 2.3 in which growth at temperature is expressed as a percentage of best growth (i.e. 24
to 28S0oTC). For comparative purposes, growth data for Macrobrachium rosenbergii have
been included. These data were generated under identical experimental conditions at
Walkamin in 1986 (Barlow, pers.comm.).
Figure 2.1. Percentage survival of Cherax quadricarinatus at five temperatures over 70 days.
5
Treatment
Temperature
(°C)
Size
20
20
L
S
24
24
Mean Growth
Standard error of
mean
n
2.37
1.83
0.23
0.17
37
34
L
S
4.89
4.13
0.43
0.35
28
29
28
28
L
S
4.86
5.16
0.43
0.46
23
29
32
32
L
S
3.84
2.88
0.35
0.27
30
40
34
34
L
S
0.92
1.32
0.50
0.75
11
7
(g)
Table 2.2. Growth statistics for Cherax quadricarinatus held for 70 days at five temperatures.
Mean size of large (L) crayfish was 1.27g and for small (S) crayfish was 0.61g.
Treatment
Temperature
(°C)
Mean Growth
(g)
Standard error of
mean
of
20
24
28
32
34
n
mean
2.11
4.50
5.03
3.29
1.08
0.15
0.28
0.33
0.22
0.22
71
57
52
70
18
Table 2.3. Growth statistics for Cherax quadricarinatus held for 70 days at five temperatures,
from one-way ANOVA, size groups pooled.
6
Figure 2.2. Growth of Cherax quadricarinatus at five temperatures over 70 days. a, mean
size at day 0 small (0.61g); b, mean size at day 0 large (1.27g).
7
Temperature °C
34
20
32
24
28
Mean Growth (g) 1.08 2.11 3.29 4.50 5.03
Table 2.4. Pairwise comparisons of means of growth after 70 days at five temperatures,
generated by ANOVA. Means underscored by the same line are not significantly different (p
< 0.01).
Figure 2.3. Relative growth performance of Cherax quadricarinatus and Macrobrachium
rosenbergii over the temperature range 20 to 35S0oTC. Maximum growth rate equivalent to
100%.
2.4
Discussion:
The results presented indicate that Cherax quadricarinatus has a broad tolerance to
temperature. Survival of juvenile crayfish, generally more specific than adults in their
temperature requirements (Mason, 1978), was similarly high over a 12S0oTC range from 20
to 32S0oTC. Although survival at 34S0oTC was poor, it is interesting to note that after 56
days, some lessening of mortality was evident suggesting acclimation. This pattern was also
apparent at the other temperatures. Such acclimation is further evidenced in the growth curves
(Fig. 2.2) which suggest increasing growth rate after day 56 at the two most extreme
8
temperatures, 20 and 34S0oTC.
The growth results are particularly instructive when compared with Macrobrachium
rosenbergii (Fig. 2.3). Although both species are tropically distributed freshwater crustaceans
with similar life habits, C. quadricarinatus has a relatively broader optimal range of
temperature. The data indicate that greater than 70% of optimal growth for C. quadricarinatus
can be achieved over a 9S0oT range (22.5 to 31.5S0oTC). By comparison, the same growth
response for M. rosenbergii is achieved over a 5S0oTC range (29.0 to 34.2S0oTC). Of
substantially greater significance is the relative position of these optimal ranges on the
temperature gradient. M. rosenbergii requires significantly higher temperatures for good
growth.
In consideration of these temperature/growth attributes and the prevailing water temperature
conditions throughout Queensland, it is apparent that C. quadricarinatus has considerably
greater geographical potential for cultivation than M. rosenbergii.
Although similar temperature/growth data are documented for other crayfish species, direct
comparisons are of little value because all of these species are sub-tropical to temperate in
distribution and consequently have lower optimal temperature ranges. An exception is the
yabbie Cherax destructor which has an optimum temperature range similar to that of C.
quadricarinatus (Mills, 1989, Carroll, 1981), despite its more southern distribution.
The temperature/growth information presented is representative of C. quadricarinatus
juveniles of the Mitchell River population. It is reasonable to assume that this information is
directly applicable to adults of the same stock. However, because genetically-based
physiological differences between C. quadricarinatus from different river systems are likely
(Austin, 1986), some minor difference in the response to temperature may exist. Such
differences are worthy of investigation, as they would assist in optimizing the suitability of
culture stock to localised climatic conditions.
9
3
3.1
SALINITY EXPERIMENTATION
Introduction:
Crayfish inhabiting riverine systems are likely at some time to encounter water with salinity
elevated beyond that of fresh water. This may occur as an animal actively or passively (during
flood) moves towards the sea, or when normally fresh water becomes saline due to
evaporation, localised geology or other mechanisms (Bayly and Williams, 1973). Freshwater
crayfish are by definition, inhabitants of fresh water, however, there are several reports of
freshwater crayfish species inhabiting brackish water with no adverse indications (Morrissy,
1978; Rundquist and Goldman, 1979; Sharfstein and Chafin, 1979; Mills and Geddes, 1980).
The physiological effect of elevated salinity on freshwater crayfish has been investigated for
several species (Kendall and Schwartz, 1964; Loyacano, 1967; Kerley and Pritchard, 1967;
Wong and Freeman, 1976a,1976b,1976c; Mantel and Farmer, 1983; Goodsell, 1984;
McMahon, 1986).
From an aquaculture perspective, the ability of a species to tolerate saline conditions has
important implications in regard to geographic potential. Many areas satisfy all site suitability
criteria with the exception that the water supply is brackish. Maximum use of these areas can
be made if salinity tolerance of prospective species is understood.
Moreover, there is evidence to suggest that some freshwater crayfish grown under saline
conditions will out-perform those grown in pure fresh water (Rundquist and Goldman, 1978).
As a preliminary investigation of the aquaculture potential of Cherax quadricarinatus, adult
crayfish were exposed to several salinities to gauge their salinity tolerance.
An additional stimulus for this experimentation was the potential for enhancing the flavour of
C. quadricarinatus, which is considered by many to be too mild. Considerable documented
information concerning penaeid prawns indicates that flavour may be improved by
conditioning animals (live) in saline solutions (McCoid et al., 1984; Papadopoulos and Finne,
1986).
3.2
Materials and Methods:
A complete randomized block experimental design was employed incorporating five salinity
treatments (0, 6, 12, 18 and 24 parts per thousand) and 4 replications. Five adult crayfish,
Cherax quadricarinatus, were assigned to each treatment in 801 glass aquaria.
Salinity treatments were prepared by incrementally adjusting fresh bore water up to the
desired salinity at 2ppt per day by the addition of filtered oceanic seawater (for 6ppt
treatment), or by incrementally adjusting filtered oceanic seawater down to the desired
salinity by the addition of fresh bore water (for 12, 18 & 24ppt treatments). Each tank was
equipped with a power filter (Fluval 203) which contained reef sand and coral rubble media,
pre-conditioned in established freshwater aquaria (0 & 12 ppt treatments) or in established
marine aquaria (12, 18 & 24 ppt treatments). Once desired salinities had been achieved,
ammonium salts were added and ammonia and nitrite were measured daily (Seatest Multi-kit)
to gauge the efficiency and maturity of the filterbed. Experimentation was initiated after
nitrite levels peaked and dropped (approximately 2 weeks).
10
Each aquaria was furnished with a 5mm depth of fine river sand across the bottom and
crayfish habitat consisting of five 20cm lengths of 75mm diameter PVC pipe. Water was
continuously aerated.
Salinity was measured daily with a refractometer (Reichert-Jung) and adjusted as necessary.
Ammonia and pH were measured manually each day and temperature every four hours by
probes connected to a datalogger (Datataker DT 100F). A 50% replacement of water was
performed in each tank at day 14. Water temperature was maintained at approximately 27°C
in all tanks with aquarium heaters (Supreme Pet 200w). Photoperiod was maintained at
14L:10D.
Adult crayfish were collected by trapping from an earthern pond at the Walkamin Research
Station and held for 2 weeks prior to experimentation in fresh bore water. 50 individuals of
each sex were chosen randomly and tagged with individually numbered plastic labels
(Hallprint) attached to the dorsal surface of the carapace with epoxy adhesive. Care was taken
to select only robust, healthy individuals in intermoult condition. These were transferred to
the experimental facility and held in fresh water. Either 2 males and 3 females, or 3 males and
2 females were assigned to each tank. Crayfish assigned to salinity treatments of 12, 18 and
24ppt were acclimated to their treatment at 6ppt per day so that all experimental animals were
introduced to their tank on the same day (day 0).
Food included a pelletised formulated diet (Cheetham Rural) and fresh aquatic weed
(Potamageton spp.), introduced ad libitum each afternoon. All crayfish were weighed at day 0
(Table 3.1) and then again at day 7, 14 and 21 at which time the experiment was terminated.
Differences in weight increase and survival among the five treatments were compared with
analysis of variance. Weight data were normally distributed and therefore suited to parametric
analyses, however, a non-parametric test (Kruskal-Wallis 1-way ANOVA) was appropriate
for survival data. Pairwise comparison of means were performed using Duncans Multiple
Range test.
The impact of salinity treatments on the flesh flavour was assessed by sensory evaluation
involving a taste panel (Chapt.8).
Salinity Treatment (ppt)
OCL (mm)
Weight (g)
N
0
6
12
18
24
48.9
(0.8)
75.4
(4.1)
20
48.0
(1.3)
75.4
(5.8)
20
43.6
(1.2)
54.3
(4.6)
20
49.2
(1.2)
77.9
(4.9)
20
45.0
(1.3)
61.3
(5.7)
20
Table 1. Mean size statistics at day 0 for treatment groups of Cherax quadricarinatus used in
salinity tolerance experimentation. OCL -orbital carapace length and weight refers to whole
wet weight. Bracketed number is the standard error of the mean.
11
3.3
Results:
Both survival and weight of Cherax quadricarinatus were affected by salinity. After 21 days,
survival was significantly reduced at 24 and 18ppt (p=0.10) (Fig. 3.1). 80% of the mortalities
occurred within the last 7 days of the experimental period, and are attributable to the
treatment effect. Crayfish at 0, 6 and 12ppt showed no adverse indications to the treatment
after 21 days. Surviving crayfish at 18 and 24ppt were noticeably lethargic and appeared to
consume less food. During the experimental period 1 female at each of 0 and 18ppt and 2
females at 6ppt spawned and carried fertilized eggs.
Weight of crayfish varied significantly (p=0.075) over the experimental period (Table 3.2).
Figure 3.1 shows the mean weight change at 7 day intervals for each of the five salinities. The
weight change, which was not always positive, may be attributed to both food intake and
osmo-regulatory events. A noticeable change in the pattern of weight change during the
second 7 day period is likely to be linked with the degradation of water quality, particularly
the increase in ammonia. This water quality problem was alleviated at day 14 by a 50% water
replacement in all tanks. The consequent improvement in water quality was reflected in
substantial weight gains over the third 7 day period. A pairwise comparison of mean weight
change after 21 days indicated that crayfish held at Oppt were significantly heavier than those
at 18ppt.
12
Salinity Treatment (ppt)
0
6
12
18
24
Mean
6.59a
4.77a,b
4.67a,b
4.18b
5.69a,b
S.E.
0.83
0.65
0.40
0.48
0.81
20
20
20
16
14
N
Table 3.2. Analysis of variance results of weight change (g) for treatment groups of Cherax
quadricarinatus used in salinity tolerance experimentation. Mean represents increase in wet
weight after 21 days. Means with the same letter are not significantly different (p < 0.05).
Figure 3.2. Cumulative mean weight change of Cherax quadricarinatus over 21 days at five
salinities. Salinity treatment units are parts per thousand.
3.4
Discussion:
Although Cherax quadricarinatus has not previously been recorded from a brackish water
environment, the results of this experimentation suggest a developed capability to tolerate
saline conditions. This is not surprising in view of the natural distribution of this species.
Large sections of river systems supporting C. quadricarinatus (Chapt.1) are ephemeral due to
13
extreme and markedly seasonal climatic conditions prevailing. Monsoonal rainfall and
consequent flooding, generally between January and April, may translocate crayfish many
hundreds of kilometres towards the sea where elevated salinities may be encountered. Dry
season evaporation is sufficiently extreme to reduce flowing streams to static and independent
water holes which may exhibit increasing salinity between June and December. Although
salinity statistics for water bodies known to support C. quadricarinatus are not available,
saline conditions in habitats typical for this species are well documented (Bayly and Williams,
1973).
The physiological mechanisms operating for C. quadricarinatus can only be hypothesised with
the existing information. Because the survival of crayfish at elevated salinities in this study
was equivalent to that for other Cherax species (Table 3.3), it may be inferred that C.
quadricarinatus is typically euryhaline and capable of at least hyper-regulating at low
salinities.
Species
C. quadricarinatus
C. quadricarinatus
C. quadricarinatus
C. destructor
C. destructor
C. destructor
C. tenuimanus
C. tenuimanus
C. tenuimanus
C. tenuimanus
Salinity
(ppt)
Period (d)
Survival
(%)
12
18
24
16.3
24.5
31.6
21.4
25.5
30.5
34.5
21
21
21
8
8
4
40
26
2.4
2.2
100
80
70
90
80
0
50
50
50
50
Source
Present Study
Present Study
Present Study
Mills & Geddes 1980
Mills & Geddes 1980
Mills & Geddes 1980
Morrissy 1978
Morrissy 1978
Morrissy 1978
Morrissy 1978
Table 3.3. Salinity tolerance data for species of Cherax.
It is apparent from the osmo-regulatory studies by Mills and Geddes (1980), Greenway and
Lawson (1982) and Goodsell (1984) that Cherax regulates blood concentration
hyperosmotically up to a species specific critical point which corresponds to an ambient
salinity of between 15 and 25ppt. After this critical point is reached, the blood concentration
follows the isosmotic line (Fig. 3.3). There is no indication from the literature of an ability
within Cherax, to hyporegulate at high salinities as described for Pacifastacus leniusculus
(Rundquist and Goldman, 1978; Wheatley and McMahon, 1983; McMahon, 1986) (Fig. 3.3)
and many other brackish water species (Panikkar, 1941). Although such an ability is
uncommon amongst freshwater crustaceans (Mills and Geddes, 1980; McMahon, 1986), its
operation in C. quadricarinatus can not be ruled out until more specific studies of osmoregulation are performed.
Although Cherax demonstrates an ability to osmoregulate up to moderately high salinities
(15-25ppt), the period of exposure to the saline conditions must also be considered. For short
periods, relatively high salinities, up to and in excess of seawater, may be tolerated. However,
protracted exposure to much lower salinities may still prove to be fatal. Comparisons between
species are therefore difficult when test procedures use both different salinities and exposure
periods.
14
Although Goodsell (1984) indicates that C. tenuimanus has greater osmo-regulatory ability,
and therefore tolerance to elevated salinity than C. destructor, Morrissy (1978) suggests an
incipient lethal limit for C. tenuimanus of 17ppt, substantially less than the median tolerance
limit (for 96h) of 29.9ppt estimated by Mills and Geddes (1980) for C. destructor.
Figure 3.3. Osmotic concentration of blood of Cherax destructor and Pacifastacus leniusculus
exposed to varying salinities, demonstrating hyper and hypo regulation. Data taken from Mills
and Geddes (1980) and McMahon (1986).
Further examination of the salinity tolerance of C. quadricarinatus should also involve
independent studies of juvenile and adult crayfish. It is clear from several studies (Morrissy,
1978; Mills and Geddes, 1980; McMahon, 1986) that juveniles are significantly less tolerant
of exposure to elevated salinity than adults.
In addition to the mortality and weight change response to salinity, qualitative assessment of
behavioural response was made towards the end of the experimental period when differences
between treatments were clearly apparent. All crayfish held at 18 and 24ppt were noticeably
lethargic when deliberately disturbed or handled. This observation is supported by those of
Mills and Geddes (1980) who found that behavioural responses of C. destructor diminished
with increasing time at moderate to high salinities, greater than 12ppt. The successful
spawning of four female crayfish in this study (0 to 18ppt) suggests that complex courtship
and mating behaviours were not impeded by the salinity.
The effect of salinity on sensory characteristics (taste) of the crayfish flesh is discussed fully
in Chapter 8. Mechanisms which lead to this effect, however, are directly linked with salinity
15
tolerance and osmo-regulatory ability. Fundamentally, osmo-regulation involves the
balancing of ionic concentration between internal body fluids and the external media. This
process involves the mobilisation of free amino acids (FAA), the levels of which are actively
altered to achieve the balance (Wheatley and McMahon, 1983; McMahon, 1986). Apparently,
the source of these FAA is the oxygen carrying molecule, haemocyanin, which is broken
down to its constituent amino acids. Because the FAA have been shown to be the major
contributors to flavour in seafood species (Hashimoto, 1965; Papadopoulos and Finne, 1986),
it has been speculated that changes in environmental salinity may be used to optimize flavour
characteristics (McCoid et al., 1984). Although most work in this area has been directed
towards penaeid prawns, its application to freshwater crayfish with naturally milder flavours
is clearly significant. Fortunately, C. quadricarinatus is sufficiently tolerant of saline
conditions to experiment in this regard.
From an aquaculture point of view, the results of this study suggest that C. quadricarinatus
may tolerate saline conditions with no adverse indications up to and possibly exceeding
12ppt. Further experimentation on relative growth performance in saline water is required
before the suitability of brackish water sites can be fully appraised. If growth at salinities of
12ppt or less is comparable to that in fresh water, there may be several significant advantages
in utilizing brackish water.
16
4
4.1
JUVENILE NUTRITION AND HABITAT
Introduction:
Within the developing freshwater crayfish aquaculture industry in Australia provision of
suitable growing conditions for juveniles has usually followed the assumption that they
require the same conditions as adults. Although adult crayfish display a clear preference for
detrital or vegetable food materials, juvenile crayfish often possess a quite different feeding
preference and generally require more animal material (Lund, 1944; Tcherkashina, 1977;
Westman et al, 1986; Ackerfors et al., 1987). In addition, the behaviour of juveniles suggests
that they are less benthic and may be equipped with only a limited array of innate behavioural
responses which can be used to locate and secure food items (Cukerzis, 1986; Doroshenko,
1979). Consequently, if adequate growth and survival are to be achieved, suitable food types
must be provided and in a form appropriate to the crayfishes behavioural abilities.
Production of juvenile C. quadricarinatus for stocking purposes, within the existing farming
industry, is carried out in earthern ponds, where naturally reproducing crayfish are
maintained. Under these circumstances juveniles are exposed to the same conditions as adults.
They are harvested periodically by pulling bundles of folded mesh material from the water in
which the young crayfish hide.
As the industry develops, demand for juveniles will increase, with concomitant demand for
high quality, uniform size, year-round availability and appropriate price. These demands
necessitate the development of intensive juvenile rearing procedures, and knowledge of
effective growing conditions is therefore essential.
Previous experience with juvenile C. quadricarinatus which were released into fibreglass
tanks at the Walkamin Research Station, indicated that under un-controlled conditions
cannibalism was very high and survival therefore low. An attempt in 1988 to simulate a
natural stream habitat consisting of a raceway, heavily stocked with an aquatic plant
(Chapt.5), also resulted in poor survival. Of approximately 70,000 juveniles stocked, less than
10% were harvested after 50 days.
Under ideal conditions juvenile crayfish will moult and grow rapidly. Consequently, their
vulnerability during ecdysis is increased considerably. Cannabilism is likely to have a severe
impact during this early life phase if suitable alternative food is not available and unless the
habitat complexity is sufficient to allow moulting to occur with minimum likelihood of intraspecific encounters.
Reported observations from the commercial industry suggested that juvenile C.
quadricarinatus make use of aquatic vegetation as a refuge, particularly free floating species
such as Water Hyacinth (Eichhornia crassipes), Salvinia or Water Lettuce (Pistia stratiodes).
The inclusion of a water plant in an aquaculture system has obvious advantages in regard to
water filtration and oxygenation. The utility of an aquatic plant as habitat for juveniles was
therefore worthy of assessment.
Under natural circumstances zooplankton has been shown to be a major component of the
food of juvenile crayfish (Tcherkashina, 1977). Alternatively, under artificial conditions,
reasonable survival and growth of juvenile crayfish has been achieved on formulated diets
(Huner et al., 1975; Celada et al., 1989). In this study a comparison was made of survival and
growth of first stage juvenile C. quadricarinatus using fresh zooplankton or a formulated
flake food, in the presence/absence of the aquatic plant Pistia.
17
4.2
Materials and Methods:
A 5 x 2 factorial arrangement of treatments was employed in a complete randomized block
experiment with x4 replication. One treatment combination was not used.
The two factors were; food (3 treatments) and presence/absence of aquatic vegetation as
habitat. Food treatments were i) fresh zooplankton, cultivated in an earthern pond and
consisting primarily of cladocerans (Moina spp.), copepods and chironomid larvae; ii) a
formulated diet (Frippak Flake), a water stable, micro-bound flaked preparation, 40% protein,
designed for larval and post-larval penaeid prawns; iii) a control receiving no food.
A free-floating plant Pistia stratiodes (Water Lettuce) was used as the habitat treatment. This
species was chosen because it is easily incorporated into small tanks, has a dense fibrous root
system providing considerable refuge for small crayfish and has been observed to support
juvenile C. quadricarinatus in aquaculture ponds (Calleja, pers.comm.). The treatment
combination of Pistia absent and no food was not incorporated because it was not likely to
produce meaningful results.
Twenty 80l glass aquaria were filled with fresh bore water and
5mm of fine river sand was spread over the bottom. Tank water was
recirculated through power filters (Fluval 203) attached to each
tank at a rate equivalent to 6 tank volumes per hour. Water was
continuously aerated and temperature maintained at S1~T25S0oTC with
submersible aquarium heaters (Supreme Pet 200w).
Two types of artificial habitat were provided in each tank. One consisted of 3cm wide strips
of fibreglass flyscreen mesh suspended from a polystyrene float, occupying approximately
15% of the tank volume. The other habitat type was made from 75mm lengths of 10mm
diameter black plastic pipe, bound together in a 5x10 unit. One unit was placed in each tank.
As both these artificial habitats had been used previously with juvenile C. quadricarinatus,
there presence enabled qualitative assessment of the relative preference for the vegetation
habitat. Tanks with Pistia present were each stocked with two individual plants of a standard
size.
Juvenile C. quadricarinatus were gathered from 2000l 'hatchery tanks' which had been
stocked previously with egg-bearing adults. Only immediate post-hatchling juveniles were
selected with a mean wet weight of 0.02g. Juvenile crayfish were held in several 10l plastic
buckets for 24hrs prior to experimental use so that unhealthy and otherwise non-robust
individuals could be eliminated. 30 crayfish were selected for each treatment replicate and
their combined wet weight measured on an electric balance (Ohaus 4000) before being
released into the aquaria. Mean starting weights were calculated from these total weights
(Table 4.1). The stocking density was equivalent to 100/mS02T
Feeding consisted of the treatment foods only. Food was provided ad libitum each afternoon
and uneaten food removed each morning. Due to poor natural light incidence in the
experimental facility, the Pistia began degenerating after some days. All plants were therefore
replaced with fresh material as was deemed necessary on days 13, 22 and 33 of the
experimental period. Discard plants were carefully dismantled to ensure no crayfish were
inadvertantly thrown out. The opportunity was taken while replacing plants, to thoroughly
clean all tanks and count surviving crayfish. Crayfish were not handled and weights were not
18
taken on these occassions. The experiment was terminated on day 39 at which time individual
crayfish were removed and weighed.
Growth was expressed as individual weight at day 39 minus the mean day 1 weight of each
tank. Survival was expressed as the proportion of crayfish alive at each count. Differences in
growth and survival among the five treatment combinations were examined with analysis of
variance. As growth data were normally distributed, parametric analyses were employed,
however, a non-parametric test (Kruskal-Wallis 1-way ANOVA) was applied to survival data.
Pairwise comparison of means were made using Duncans Multiple Range test.
Tank
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
Total Weight
0.50
0.62
0.69
0.52
0.63
0.58
0.62
0.59
0.80
0.57
Mean Weight 0.017 0.021 0.023 0.017 0.021 0.019 0.021 0.020 0.027 0.019
Tank
T11
T12
T13
T14
T15
T16
T17
T18
T19
T20
Total Weight
0.61
0.62
0.75
0.57
0.69
0.57
0.67
0.58
0.57
0.63
Mean Weight 0.020 0.021 0.025 0.019 0.023 0.019 0.022 0.019 0.019 0.021
Table 4.1. Total wet weight (g) and mean individual weight (g) of 30 juvenile Cherax
quadricarinatus assigned to each of the 20 tanks in the nutrition/habitat experiment.
4.3
Results:
Both survival and growth of juvenile C. quadricarinatus were significantly influenced by the
type of food and habitat provided.
Mean survival of crayfish after 39 days ranged from S1~T30% to S1~T70%
(Fig.4.1) (Table 4.2). Analysis of variance indicated significant variability in survival (p <
0.05), although the cause of this was not clear. Flake food and Pistia present produced the
best survival (66%), while Zooplankton and Pistia produced the lowest (28%). Statistical
analyses were limited by the non-parametric nature of the data, however, it was clear that
survival results were consistent within treatment combinations (replicates).
Growth occurred in all treatments (Fig.4.2). The mean weight increase after 39 days ranged
from 0.16g (800%) to 0.46g (2300%) (Table 4.2). Significant variability in growth between
treatment combinations was apparent (p < 0.001). A two-way analysis of variance was
performed to examine the individual effect of Pistia presence/ absence and food type, and any
interactive effect between them. Both Pistia presence and food type each had a significant
effect on growth (p < 0.01) and significant interaction was also measured (p < 0.05).
Interpretation of these results is not entirely straightforward. Figure 4.3 illustrates the results
of pairwise comparison of mean growth. Growth under treatments: No food and Pistia; and
Flake food only, was clearly less than that under the 3 other treatment combinations. Presence
19
of Pistia appeared to have a beneficial effect when additional food was present, but did not
provide for good growth by itself. As a food zooplankton produced good growth both with
and without Pistia present. Flake food however produced comparatively good growth in the
presence of Pistia, but appeared to be inadequate without the plant.
Growth results were closely echoed by survival results (Table 4.2) with one exception; the
combination of zooplankton and Pistia, which produced good growth, but resulted in poor
survival.
4.4
Discussion:
Due to an interactive effect between Pistia and zooplankton, the results of this experiment
require careful interpretation. Zooplankton was clearly superior to the flake preparation as a
food, although growth with flake food was still considerable. The nature of the interaction
between the zooplankton and plant was not clear.
Qualitative assessment of the health of the Pistia during the experimental period suggested
that those plants in tanks receiving zooplankton were in the poorest condition and appeared to
degenerate most rapidly. Although all Pistia plants were replaced regularly, it is possible that
the degenerative process
Figure 4.1. Mean survival of juvenile Cherax quadricarinatus over 39 days using 5
combinations of food and habitat. PF - Flake food, Pistia present, Z - Zooplankton food only,
F - Flake food only, P - No food, Pistia present, PZ - Zooplankton food, Pistia present.
Statistic
20
P
F
PF
Z
PZ
MeanWeight (g) 0.16 0.18 0.34 0.36 0.46
Survival (%)
39
45
66
59
28
N
47
54
79
71
34
Table 4.2. Growth and survival statistics for juvenile Cherax quadricarinatus after 39 days
using 5 combinations of food and habitat. P - No food, Pistia present, F - Flake food only, PF
- Flake food, Pistia present, Z - Zooplankton food only, PZ - Zooplankton food, Pistia
present.
Figure 4.2. Mean growth of Cherax quadricarinatus after 39 days using 5 combinations of
food and habitat. PZ - Zooplankton food, Pistia present, Z - Zooplankton food only, PF Flake food, Pistia present, F - Flake food only, P - No food, Pistia present.
21
Figure 4.3. Mean and 95% confidence intervals of growth of juvenile Cherax
quadricarinatus after 39 days using 5 combinations of food and habitat. P - No food, Pistia
present, Z - Zooplankton food only, F - Flake food only, PF - Flake food, Pistia present, PZ Zooplankton food, Pistia present.
influenced the survival of the crayfish, possibly through the release of some chemical. This
explanation is not entirely satisfactory because a toxin is likely to have sub-lethal effect
which was not indicated by the superior growth of the surviving individuals. Ammonia and
pH levels in zooplankton/Pistia tanks were equivalent to those for other treatment
combinations.
Inclusion of living plants in aquaculture systems has been suggested or trialled before (Anon.,
1984; Corpron and Armstrong, 1983), usually for their water cleaning capacity. However,
their utility as a habitat for juvenile crayfish has not previously been documented. The
suitability of Pistia as a habitat for juvenile C. quadricarinatus was not supported by this
study. The interactive effect with zooplankton may be overcome by providing natural light
conditions under which the plant should not degenerate. However, there were other more
practical reasons why presence of Pistia was undesirable. Harvesting of crayfish from the
plant or from tanks containing the plant was particularly difficult (Chapt.5). Individuals taking
refuge within the root system could only be effectively removed by completely dismantling
the plant. Those crayfish remaining in the tank water took refuge beneath a fine organic mat
on the tank floor, created by the continual precipitation of root hairs from the plant above.
Accumulation of organic detritus beneath floating vegetation can be excessive (Timmer and
Weldon, 1967). Any productivity benefit gained from the presence of Pistia is exceeded by
greatly increased handling difficulties while harvesting.
Qualitative assessment of the relative use of the Pistia as habitat in comparison to the
22
artificial habitats provided indicated that no clear preference was apparent. The fly-screen
mesh habitat, which effectively simulates characteristics of submerged macrophytes, appeared
to be as equally used as Pistia, when present. Although the pipe habitat appeared least often
used, these results may be influenced by relative availability. For the mesh habitat, an edge
preference appeared to operate, similar to that described for juvenile Macrobrachium
rosenbergii (Smith and Sandifer, 1979). Notwithstanding possible nutritional benefits of fresh
plant material, provision of habitat for juvenile C. quadricarinatus may be most adequately
effected by artificial materials. Smith and Sandifer (1979) have demonstrated that particular
configurations of artificial habitats are superior to natural materials and can significantly
increase productivity of intensive juvenile prawn rearing systems.
Growth of juvenile C. quadricarinatus on both zooplankton and flake food diets was
improved in the presence of Pistia suggesting that a nutritional benefit was conferred by the
plant. Several authors have documented the nutritional benefit of supplemented plant material
in the diet of crustaceans (Hessen and Skurdal, 1986; Huner, 1984; Harpaz and Schmalbach,
1986; Celada et al., 1989). The pond reared zooplankton used in this study would have
included some plant material, as phytoplankton in the gut. However, fresh plant material may
provide nutritional elements not available in animal matter.
Similarly, a major advantage of the zooplankton over the flake diet was its fresh (live) state. It
is well established that most forms of processing decrease the nutritional quality of fresh
foods (Grabner, et al., 1981; Celada et al., 1989).
It was apparent from this study and previous observations that nutrition and habitat are the
two most important parameters in providing suitable conditions for cultivation of juvenile C.
quadricarinatus . Although the prepared flake diet produced reasonable growth, its
performance was well exceeded by fresh zooplankton. The plant material provided a small
nutritional benefit, however, its effectiveness as a habitat was poor. The addition of vegetable
material as a nutritional supplement may be advantageous, although from a practical point of
view not in the form of whole free floating plants. Artificial materials may be equally or more
acceptable as habitat, and are easier to maintain. The best survival rates were relatively good
in comparison to those documented for juvenile crayfish (Kossakowski and Kossakowski,
1983; Pursiainen, et al., 1983; Celada et al, 1989), however, from an aquaculture perspective
considerable improvement is desirable.
23
5
5.1
DEVELOPMENT OF HATCHERY/NURSERY PROCEDURES
Introduction:
There has been considerable interest in the development of hatchery and nursery technology
for freshwater crayfish. This interest has been stimulated with different objectives in mind, for
different species. In Europe, for example, decimation of native stocks of Astacus astacus by
crayfish plague, stimulated the notion of restocking programs. Development of hatchery
systems was therefore necessary to produce young, disease-free crayfish (Huner and
Lindqvist, 1987; Keller, 1987). These systems have been established and are currently
producing significant numbers of juvenile A. astacus and other introduced species such as
Pacifastacus leniusculus, under intensive conditions.
In contrast, the substantial southern United States crayfish farming industry has developed
without the application of intensive hatchery or nursery procedures, although they have been
suggested and investigated (Nelson and Dendy, 1979; Huner and Barr, 1984; Trimble and
Gaude, 1988). Under the extensive methods applied in this industry it would appear that
supplementation of natural pond production with intensively reared juveniles is not yet
economically justified.
Australian crayfish culture is represented by a variety of approaches. Hatcheries have been
used, but generally to the extent of producing egg-bearing females which are stocked to
growout ponds. Intensive production of egg-bearing females or of juveniles, in the cultivation
of C. quadricarinatus, has been considered unnecessary, and with good reason. This species
has a broad reproductive season which may extend for more than 6 months, it may breed
successively through this season and has a large reproductive capacity, producing between
200 and 1000 eggs per batch. Successful and sufficient production of juveniles has been
achieved by maintaining reproducing populations of C. quadricarinatus in earthern ponds,
from which the juveniles are periodically harvested. Bundles of plastic mesh are distributed
throughout the pond, and held on the bottom by a weight. Juveniles make use of these
'refuges', and are harvested in considerable numbers by retrieving the bundles and shaking
them out. An accurate measure of this systems efficiency is not possible, however, it is
unlikely that survival is better than 5 to 10%. Moreover, growth is extremely variable.
This system's disadvantages are: i) does not permit production during non-reproductive
season (S1~T6 months), ii) production is entirely unpredictable, iii) harvesting is labour
intensive, iv) production of extreme variability in size, v) inefficient.
As the industry develops, it is likely that increasing importance will be placed on: i) yearround availability of juveniles, ii) uniformity of size of juveniles for stocking, iii) quality of
juveniles, iv) optimal usage of available land area.
Consequently, hatchery and nursery procedures appropriate for C. quadricarinatus were
investigated. The primary objectives were to develop broodstock handling procedures,
stimulate C. quadricarinatus to spawn during the non-reproductive season, maintain eggbearing females through the incubation period, and on-grow 'hatchling' crayfish to a size
suitable for stocking. This last objective was considered necessary to ensure that juveniles
were large enough to be bulk handled without significant mortality and to minimise predation
mortality due to dragonfly nymphs and other aquatic insects in the growout ponds.
Preliminary information necessary to achieve these objectives was available in the literature.
Studies of the reproductive biology of various freshwater crayfish provide useful information
24
on maturation physiology, mating behaviour, egg laying and incubation processes and posthatching aspects (Hopkins, 1967; Mason, 1970a, 1970b, 1977, 1978; Morrissy, 1970, 1975;
Bretonne and Avault, 1977; Pippitt, 1977; Ameyaw-Akumfi, 1981; Bechler, 1981; Lahti and
Lindqvist, 1983; Woodlock and Reynolds, 1988). In addition, specific studies of induced
spawning of various crustaceans were examined (Dendy, 1978; Quackenbush and Herrnkind,
1981; Lee and Fielder, 1982; Hedgecock, 1983; Aiken and Waddy, 1985; Browdy and
Samocha, 1986; Huner and Lindqvist, 1985; Westin and Gydemo, 1986, Trimble and Gaude,
1988). These studies indicate that manipulations of temperature and photoperiod are the most
effective means of stimulating un-seasonal spawning. The relative importance of temperature
or photoperiod and the nature of the manipulations are reasonably species specific, but in
general they involve mimicing natural fluctuations in these parameters on an abbreviated time
scale.
Hatchery techniques applied to lobsters, Homarus (Chang and Conklin, 1983),
Macrobrachium rosenbergii (Aquacop, 1983; Malecha, 1983b) and various species of
freshwater crayfish (Cuellar and Coll, 1979; Nelson and Dendy, 1978, 1979; Keller, 1987;
Trimble and Gaude, 1988) were considered in determining a system for C. quadricarinatus.
Similarly, juvenile rearing procedures employed for M. rosenbergii (Stern et al., 1976;
Malecha, 1983b; Mulla and Rouse, 1985) and freshwater crayfish (Mason, 1978; Nelson and
Dendy, 1978, 1979; Pursiainen et al., 1983; Trimble and Gaude, 1988; Celada et al., 1989)
were evaluated before developing the systems trialled in this study.
The procedures developed and described below, were generated over two years and two
separate production seasons. Although the second season incorporated modifications and
improvements over the first, and produced better results, all procedures proved instructive and
both seasons are fully described.
5.2
Materials and Methods:
1988 Production
Broodstock: In excess of 500 male and female C. quadricarinatus were collected by
trapping from a natural dam near Walkamin (Mitchell River Stock). They were held in large
outdoor concrete tanks, with shadecloth covers, aeration and continuous water replacement.
Food was provided every few days, consisting primarily of aquatic vegetation (Potamageton)
and varying small quantities of prawn/fish flesh, liver, various vegetables and pelleted rations.
A sample of approximately 70 females was used for developing an in vivo (while alive) ovary
staging technique. These females were dissected to determine the accuracy of the technique.
Male and female crayfish were selected randomly from the broodstock tanks for introduction
to the hatchery. Care was taken to select only healthy and robust individuals and females were
only selected if ovary staging indicated mature/maturing ovaries. Selected females were
tagged with an individually numbered plastic label (Hallprint Australia) attached to the
carapace with super-glue, and their weight and carapace length were recorded.
Hatchery: The hatchery consisted of a small masonry-block building with floor space
sufficient to incorporate six 2.0m diameter fibreglass tanks. Each tank was provided with a
5mm depth of fine river sand and various lengths of PVC pipe as habitat. Water was sourced
from a bore and delivered to each tank by overhead lines. It was sprayed into each tank to
provide aeration and a current sufficient to move debris towards a central overflow pipe.
25
Flow-rate was adjusted to maintain an exchange of 100% twice per day. Depth was
maintained at approximately 40cm. Continuous compressed air aeration was provided in each
tank.
The bore water is characterised by a constant year-round temperature of 25 to 26S0oTC, and
arrived at the hatchery with little loss of heat. This temperature was 5 to 10S0oTC warmer
than the ambient water temperature of the broodstock tanks and the collection site, at the time
of initiating the hatchery procedures (July-August). Fluorescent ceiling lights were connected
to a time switch which enabled 14:10 hour Light:Dark photoperiod, providing an additional 3
to 4 hours of light over ambient conditions. These temperature and photoperiod modifications
represented the controlled environmental conditions considered necessary to stimulate
spawning. These conditions effectively mimic those prevailing naturally during summer.
Selected broodstock were introduced to the hatchery tanks over 24 hours via a series of water
baths of increasing temperature. Fourteen females were placed in each tank. Males were
introduced at one of three ratios; 14:14, 7:14 or 5:14 (M:F).
Crayfish were maintained in these tanks on a diet consisting primarily of Potamageton weed.
All females were checked regularly (2-3 times/week) and berried individuals were transferred
to 80l glass aquaria under similar environmental conditions. Fresh female broodstock were
introduced to hatchery tanks to replace the berried ones removed. Males were replaced
periodically.
Frequent observations were made of the berried females and in particular, the egg mass.
Information was recorded on the colour and other morphological characteristics of the eggs as
incubation progressed, enabling the definition of discrete stages. From this, a schedule of
development was generated. The data permitted 2 approaches for defining incubation timing,
i) individual stage duration, when observations were sufficiently frequent to witness
successive stages, and ii) cumulative stage duration, when less frequent observations provided
an interval between 2 non-successive stages.
As eggs reached an advanced stage of development, just prior to release, females were
transferred to a nursery tank.
Nursery: A simulated stream environment was prepared as a nursery for rearing the juvenile
crayfish. This was achieved by constructing a long narrow (raceway) tank, consisting of a
heavy plastic liner suspended from a framework of steel water pipe with hardiplank walls.
Dimensions were 1m high by 1m wide by 25m long. Bore water was introduced at one end
and a screened overflow pipe at the opposite end enabled a slow current to flow.
Water depth was maintained at approximately 60cm and the water surface was covered with
the free-floating aquatic plant, Pistia stratiodes ('Water Lettuce'). The water depth was
sufficient to leave about 10cm of free space beneath the root system of the plant mass.
Berried females from the glass aquaria were individually introduced into releasing chambers
placed in the nursery tank. These chambers consisted of inverted plastic flower pots, with a
plastic mesh bottom and attached floatation. Berried females were checked every 2 to 3 days
and removed once all of the hatchlings had been released.
The nursery tank received no supplemental feeding. Harvesting occurred on one occasion
only. All plants were removed and their roots flushed with water to remove juvenile crayfish.
26
The tank water was siphoned through a fine mesh screen.
1989 Production
Based on the previous years experience and the completion of further experimentation,
hatchery/nursery procedures during 1989 were improved and streamlined, although otherwise
were similar to those described above. Procedures were initiated much earlier in the year to
ensure availability of juveniles for pond stocking at the beginning of summer, as suggested in
Chapt.7.
Broodstock: The majority of broodstock were gathered from a 'broodstock' pond at
Walkamin Research Station, which had been stocked with 1988 broodstock crayfish and
considerable numbers of wild stock. Those gathered were held in concrete tanks for a
quarantine period of 1 week. Subsequent to this, individuals were selected according to their
health and vigour, and ensuring that ovaries were either maturing or mature (stage 2 or 3). All
females were tagged and their weight and carapace length recorded.
Hatchery: Tank and plumbing arrangements were as described above. Each tank was
stocked in a similar manner, with 16 females and 4 males per tank. Tank stock were
segregated according to their size, such that the largest 16 females were stocked together and
so forth. Care was taken to provide males of nearest equivalent size to the females of each
tank.
Bore water temperature was boosted by the installation of aquarium heaters to each tank.
These resulted in a 1 to 2°C increase. Light regime was maintained at 14:10 hours L:D.
Fresh Potamageton weed was provided weekly in sufficient quantity to provide excess food
until the next change. Barastoc yabbie pellets were provided occasionally.
Females were checked once per week, but otherwise not disturbed. Once individuals were
known to be berried, their tag number was noted and they were left undisturbed for a period
sufficient to allow incubation to proceed to stage 6 to 7. Individual stage duration was
therefore not determined, although total incubation period was. Females calculated to be
nearing stage 6 to 7 were checked and if confirmed, were transferred to nursery tanks. They
were not replaced.
As routine checking of females progressed, it was evident that changes in the state of the
pleopods occurred prior to spawning. To ascertain the significance of this, 3 stages of pleopod
appearance were defined and recorded weekly for all unberried females.
Nursery: Nursery arrangements were based on the results of juvenile nutrition/habitat
experimentation (Chapt.4). Sixteen fibreglass tanks, 1.8m by 1.0m, were installed in a
greenhouse covered in shadecloth. Each tank had a double-layered shadecloth cover. Bore
water was supplied by overhead lines and introduced at a rate sufficient to exchange 100% of
tank water twice per day. Tanks were furnished with 5mm of fine river sand and equipped
with 2 habitat types to maximise surface area and available edges, as suggested for juvenile
Macrobrachium rosenbergii (Smith and Sandifer, 1979). The first consisted of fibreglass flyscreen mesh strips, 3cm wide, suspended from polystyrene floats. These occupied
approximately 20% of the water volume. The second habitat type was that described by Smith
and Sandifer (1979) as the most effective for M. rosenbergii. Each unit consisted of a timber
27
frame 100cm by 30cm by 30cm, with 3cm wide strips of fibreglass fly-screen mesh woven
horizontally through plastic trellis mesh attached to two of the longitudinal sides. Two units
were installed in each tank, occupying approximately 50% of the water volume.
A fine-mesh screen covered the outlet in the sump of each tank. Water level was controlled by
an external standpipe situated above a drainage canal. Depth was maintained at 30cm.
Berried females of a similar late stage of egg development (stage 7) were introduced to the
nursery tanks together, to minimise the difference in release time. Between 3 and 5 females
were stocked to each tank. Release chambers were not used. Females were checked every few
days and removed when all of the young had been released.
Food consisted of fresh or frozen (fresh) zooplankton harvested from earthern ponds at
Walkamin Research Station, and a formulated flake diet (Frippak). Zooplankton consisted
primarily of cladocerans (Moina species), copepods and chironomid larvae, and was provided
each morning. Flake food was added each afternoon. Food was provided every day at an
increasing rate based on observations of excess food. Because of the convenience of
stockpiling frozen zooplankton and its ease of handling, 4 tanks received all of their
zooplankton ration in frozen form, while others received frozen only when fresh was
unavailable.
Sampling of juvenile crayfish throughout the nursery period provided data for growth
estimates. When the mean size of each tank population achieved 0.1 to 0.3g or greater, the
tank was harvested. Harvesting involved the removal of habitats, from which the juvenile
crayfish were easily dislodged, and slow drainage of the water through a 2mm sieve.
Because the period of growth for each tank was different, direct comparisons of growth
achieved were not valid. Consequently, growth data were transformed to a daily growth index
where;
Daily Growth Index = (Mean Harvest Size / Growth Period) x 1000
This index represents the mean daily growth increment in milligrams. Differences among
tanks were then investigated using analysis of variance, and means comparisons were made
with Duncan's Multiple Range test.
5.3
Results:
1988 Production
Broodstock: An ovary staging technique was developed in which the anterior portion of the
body is held firmly and the abdomen is curled under so that the transparent connective
membrane between the carapace and abdomen is exposed. Using a concentrated light source,
and viewing anteriorly into the body chamber, macroscopic features of ovarian development
can be discerned. Subsequent dissection of 70 staged individuals enabled clarification of
features observed in vivo. Three stages of ovarian development were considered discernable
with a high probability of accuracy; 1) no ovary discernable - IMMATURE, 2) ovary
apparent, individual ova not discernable - MATURING, 3) ovary easily visible (olive green),
individual ova apparent - MATURE.
28
Using this technique, maturing and mature females were chosen for the hatchery. Between
27/07/88 and 07/10/88 some 198 females were introduced to the hatchery, ranging in size
from 31.0 to 161.0 g.
Hatchery: Over the 127 day period from 27/07/88 to 02/12/88, 167 females (84%)
successfully mated and produced eggs. There was no apparent difference in the mating
success between tanks, with different ratios of male:female. The interval from introduction to
the hatchery (and the controlled environment), to spawning and egg-bearing ranged from less
than 7 days to in excess of 100 days. A frequency distribution of number of weeks to
spawning/egg bearing is presented in Fig.5.1. The lesser frequency for 3 weeks in comparison
to both 2 and 4 weeks is an anomaly attributable to the frequency of observations. It is clear
nevertheless, that a major proportion of individuals spawn within a period 2 to 4 weeks after
being introduced to the hatchery environment. This 'conditioning period' is likely to be
necessary to achieve full reproductive maturity and spawning readiness.
Figure 5.1. Percentage frequency of spawning of female Cherax quadricarinatus at weekly
intervals after exposure to increased temperature and photoperiod within a controlled
environment hatchery. 1988 production season.
Identification of berried females within the hatchery tanks was made relatively easy by
associated behavioural changes. Newly berried females were considerably more passive and
easily captured and were always observed to have their abdomen tightly curled ventrally,
concealing the egg mass entirely. Some females displaying these characteristics but not
berried were presumed to have been in a state of readiness to mate imminently,
unsuccessfully mated, or successfully mated but interrupted prior to egg release. In the latter
case, the spermatophore was clearly evident on the sternum of the female, between the
walking legs. It usually covered the entire sternum, was opaque white in colour and quite firm
and elastic. Females bearing eggs seldom had sperm remaining, suggesting that the
spermatophore persists for a few days at most.
29
Most berried females were transferred to glass aquaria, where closer and more frequent
observations were possible. At egg release (stage 1), eggs were olive green, opaque,
approximately 2mm long and 1mm wide. Distinct colour changes and other orphological
developments were evident as incubation progressed. Seven discrete stages were recognised
and their mean individual duration estimated from the observations made (Table 5.1, Fig.5.2).
In addition, where observations were less frequent, the interval between non-successive stages
was recorded, providing a schedule of cumulative development time (Table 5.2, Fig.5.3).
Egg Stage
Statistic
1
Mean
14.0 6.0 10.2 7.2
Std Deviation 3.6
2
3
1.6 4.1
4
2.7
5
6
7
4.9
14.3 23.7
2.7
7.0
10.3
Maximum
22.0 8.0 19.0 12.0 14.0 26.0 45.0
Minimum
4.0
3.0 3.0
4.0
1.0
2.0
5.0
N
43
11
26
17
67
71
38
Table 5.1. Individual stage duration (days) of each of 7 stages of egg development of Cherax
quadricarinatus, during external incubation. Stages are distinguished by morphological
characteristics, explained in the text.
Figure 5.2. Individual stage duration (mean days) of each of 7 stages in the egg development
of Cherax quadricarinatus, during external incubation. Distinguishing morphological
30
characteristics of each stage are presented, and explained further in the text.
Egg Stage Interval
Statistic
S to 3
S to 4
S to 5
S to 6
S to 7
Total
Mean
16.1
26.9
33.0
35.1
49.6
72.1
Std Deviation 4.2
4.7
5.2
3.3
8.8
7.5
Maximum
24.0
34.0
42.0
45.0
72.0
84.0
Minimum
10.0
16.0
20.0
30.0
34.0
47.0
N
48
66
29
65
82
56
Table 5.2. Cumulative stage duration (days) in egg development of Cherax quadricarinatus
during external incubation. S refers to spawning and egg release. Egg stages are distinguished
by morphological characteristics explained in the text. Total indicates interval from spawning
to detachment of young from the maternal pleopods.
Figure 5.3. Cumulative stage duration (mean days) of each of 7 stages in the egg
development of Cherax quadricarinatus, during external incubation. Distinguishing
morphological characteristics of each stage are presented, and explained further in the text.
31
Stage 2 was characterised by dark brown coloration and considerable inflation of the eggs,
such that they became more rounded. This stage was not often seen because of its short
duration, and may not occur for all individuals. In such cases, colour may change directly to
yellow/orange (stage 3). During this third stage the egg remains opaque with no visible larval
development, however, the subsequent fourth stage is characterised by some translucency of
the egg, a colour shift towards red and sometimes dark red, and the suggestion of varying
density of material within the egg.
Stage 5 was clearly distinguished by the appearance of the eyes as dense black spots, although
these may be difficult to discern when the underlying egg colour is dark red. Only a few days
after the eyes appear, appendages (legs and antennae) become visible beneath the eyes (stage
6). The red material is now more clearly distinguished as a yolk sack on the dorsal surface of
the confined larvae. During this stage, the egg case splits open progressively revealing the
appendages. The redness disappears as the entire juvenile crayfish sheds the egg case
completely in stage 7, appropriately described as 'hatched and attached'. The young crayfish,
now fully recognisable, remains in an inverted position attached to the pleopod margin by a
twisted connective of fine hairs (setae). This represents the last stage of the incubation after
which the young crayfish begin their independent life.
Although temperature and water quality conditions were maintained at optimal levels, the
disturbance to the crayfish from continuous observations and frequent handling may have
protracted the incubation. Consequently, the duration of stages as illustrated in Figures 5.2
and 5.3, may be shortened under more ideal conditions with minimal disturbance. The
minimum durations presented in Tables 5.1 and 5.2 indicate that this is possible.
Over the period of hatchery production, 26 abortions (15.6%) and 1 mortality occurred,
possibly reflecting the level of disturbance as mentioned above. Nevertheless, 140 individuals
(83.8%) completed their incubation, confirming the resilience of this species.
Nursery: A simulated stream environment created in the nursery tank was established
approximately 3 weeks prior to the stocking of the first berried female. Water lettuce (Pistia)
was obtained from a local dam, and thrived in the nursery tank conditions. As time to
spawning and incubation period were both variable, availability of berried females (stage 7)
for the nursery tank was somewhat protracted. Between the 16/09/88 and 16/11/88, 99 berried
females were introduced to the nursery tank and removed after the release of young.
Subsequent fecundity estimates indicated that an estimated 45,000 juveniles had been
stocked.
Harvesting took place on the 06/12/88. Approximately 6,000 (13.3%) juvenile crayfish had
survived and were removed, of which the majority were 0.04g. There were about 200
juveniles in excess of 2.0g.
Harvesting was extremely laborious. Individual Pistia plants required dismembering to ensure
that cryptic juveniles were gathered. Organic debris, consisting primarily of fine root hairs,
had accumulated on the tank bottom, making siphoning of the tank water very difficult.
Despite the poor production, the perceived advantages of a living plant in the nursery system
stimulated the initiation of a juvenile nutrition/habitat experiment (Chapt.4).
32
1989 Production
Broodstock: Broodstock were removed from the broodstock pond in early May. Ninety-six
females were selected for the hatchery ranging in size from 49.5 to 166.0g.
Hatchery: All crayfish were introduced to the hatchery tanks on the 29/05/89. First spawning
occurred 2 weeks later, although only 3 crayfish had spawned up to the fourth week (Fig.5.4).
Thereafter, spawning frequency was reasonably consistent, so that after 10 weeks, 85% of all
broodstock had spawned. The hatchery was closed on the 21/09/89 at which time, all nursery
tanks had been stocked, and 93 (97%) of the original 96 females had spawned. No mortalities
were recorded, although 4 females did abort their eggs during incubation.
Incubation period from spawning through to release of young ranged from 56 to 71 days with
a mean of 66.3 days. There is apparently little variability in incubation period between
individuals. Water temperature in the hatchery ranged from a mean minimum of 24.5S0oTC
to a mean maximum of 27.6S0oTC. It is possible that incubation may be shortened at a higher
mean temperature.
Figure 5.4. Frequency of spawning of female Cherax quadricarinatus at weekly intervals
after exposure to increased temperature and photoperiod within a controlled environment
hatchery. 1989 production season.
A clear sequence of development in pleopod appearance was discernable for female
broodstock prior to spawning. Because of the 7 day interval between observations, it was not
possible to
quantify the timing involved, however, it was clear that over a period of at least some days
prior to spawning, the pleopods were groomed and cleaned spotlessly so that they resembled
those of a newly moulted individual. The mechanism enabling this was not clear, however, it
33
certainly did not involve moulting as the intact carapace tags confirmed. A secreted chemical
process is probable.
Fourteen females from the hatchery were sacrificed for fecundity estimation. Egg
development stage at the time of counting varied from stage 1 to 6. Eggs were counted
directly, providing data from which a predictive function was generated (Fig.5.5);
Log10 Egg Number = 2.267 x (Log10 Carapace length) - 1.12
Nursery: Seventy-three berried females were stocked to the nursery tanks from the 10/08/89
to 21/09/89. Between 1 and 3 weeks were required for juveniles to release, after which the
females were removed. Release dates were recorded from when the last female of each tank
was removed (Table 5.3).
Numbers of juveniles stocked to each tank were estimated from the fecundity function
described above, and ranged from 1,764 to 3,315. These were equivalent to stocking densities
of between 980 and 1,842 per mS02T.
Feeding was initiated with 10.0g (wet weight) of zooplankton and 1.0g of flake daily. This
represented a feeding rate of 22.5% and 2.2% of stocked biomass respectively (Table 5.4).
This was equivalent to a total dry weight rate of 3.2% of biomass per day. Feeding rate was
progressively increased and adjusted according to observed excess of food each morning.
Final feeding rates, prior to harvest, presented in Table 5.4, indicate that the quantity of
zooplankton increased to a mean of 81.3% of biomass, and flake food to 3.0%. This
represented a total dry weight feeding rate of approximately 6.0% of biomass per day.
Water conditions in regard to temperature and pH remained reasonably constant throughout
the production period. Mean maximum and minimum temperatures were 25.7 and 22.1S0oTC
respectively. pH ranged from 7.6 to 7.9. Due to the high exchange rate, water quality
problems were not encountered.
Periodic sampling of tanks provided mean size at time data which were incorporated with
mean harvest weight data to generate a growth plot (Fig.5.6). Growth of juvenile crayfish was
successfully explained by an exponential function of the form;
Weight (g) = 0.0221 x e(0.05561 x Age(days))
The spread of data in the growth plot (Fig.5.6) suggests great variability in the performance of
each tank. This was also reflected in the variability between tanks in survival and mean size at
harvest (Table 5.3). Two tanks performed particularly poorly and can be excluded from the
analyses. These were tanks 2 and 10 which suffered from a sudden and heavy infestation of
34
Figure 5.5. Relationship between egg number and carapace length (mm) of Cherax
quadricarinatus. Egg counts were made of the external egg mass ('berry') at egg stage 1-6
(see text).
Tank
Release
Date
Number
Stocked
Density
Harvest
Date
N/m²
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
24/08/89
05/10/89
08/09/89
08/09/89
13/09/89
13/09/89
21/09/89
10/10/89
10/10/89
03/10/89
03/10/89
15/10/89
27/09/89
15/10/89
13/09/89
21/09/89
1,784
3,315
2,173
1,860
1,831
1,911
2,466
3,121
2,391
2,084
2,326
2,596
2,677
2,377
2,119
1,764
991
1,842
1,207
1,033
1,017
1,062
1,370
1,734
1,328
1.158
1,292
1,442
1,487
1,321
1,177
980
13/10/89
16/11/89
17/10/89
16/10/89
17/10/89
20/10/89
27/10/89
08/11/89
16/11/89
15/11/89
15/11/89
15/11/89
08/11/89
08/11/89
23/10/89
23/10/89
Period Harvest
(days)
N
Mean
Size
(g)
50
42
39
38
34
37
36
28
37
43
43
30
41
23
40
32
660
144
687
1,016
779
914
1,756
1,057
888
177
1,326
2,183
1,401
1,320
1,280
1,100
0.305
0.119
0.267
0.370
0.167
0.236
0.156
0.168
0.367
0.077
0.108
0.135
0.427
0.198
0.254
0.168
Survival
37.0
4.3
31.6
54.6
42.5
47.8
71.2
33.9
37.1
8.5
57.0
84.1
52.3
55.5
60.4
62.4
(%)
35
Table 5.3. Production statistics for nursery phase of Cherax quadricarinatus.
Tank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Mean
Initial Daily Ration
Final Daily Ration
Flake
Zooplankton
Flake
Zooplankton
2.8
1.5
2.3
2.7
2.7
2.6
2.0
1.6
2.1
2.4
2.1
1.9
1.9
2.1
2.4
2.8
2.2
28.0
15.1
23.0
26.9
27.3
26.1
20.2
16.0
20.9
24.0
21.5
19.3
18.7
21.0
23.6
28.3
22.5
3.5
23.0^
2.7
2.4
3.8
2.3
2.6
5.6
2.5
36.7^
2.8
1.4
2.0
4.6
2.5
3.8
3.0
50.0
1167.0^
109.0
26.6
76.9
46.3
73.0
112.6
61.4
1467.0^
139.7
67.9
50.1
154.6
61.5
108.2
81.3
Frozen
Zooplankton
7
23
2
8
12
19
20
18
34
34
99
99
100
100
36
36
Period
days
50
42
39
38
34
37
36
28
37
43
43
30
41
23
40
32
Total
(g)
Flake
Zooplankton
194
150
183
187
123
148
197
195
198
142
132
132
302
113
251
170
4,464
6,460
3,530
3,348
3,338
3,638
4,278
4,882
5,972
5,600
5,796
5,796
6,363
4,652
4,155
3,564
Table 5.4. Feeding regime for nursery production of Cherax quadricarinatus. Daily rations
are presented as percentages of biomass. Zooplankton ration based on wet weight. Frozen
zooplankton indicates the percentage of the zooplankton diet that was provided frozen rather
than fresh. ^ excluded from calculation of mean.
36
Figure 5.6. Relationship between weight and age of juvenile C. quadricarinatus under
intensive nursery conditions. Based on periodic sampling of all nursery tanks. Growth curve
represents 'best fit' exponential function where,
Weight (g) = 0.0221 x e(0.05561 x Age(days))
Corixid bugs ('water-boatmen'). It is assumed that these predatory bugs were inadvertently
introduced with the fresh zooplankton. Survival in the other tanks ranged from 31.6 to 84.1%
with a mean of 52%. Although this was less than expected
and there were no clear reasons for the mortality, it is a significant increase over that likely to
occur in nature or in pond cultivation of juveniles.
It was apparent through the nursery production period that those tanks receiving a
preponderance of frozen zooplankton (rather than fresh) had relatively greater numbers of
crayfish. Correlation analysis (Spearman Rank) indicated a significant positive correlation
between proportion of zooplankton diet frozen and survival (p<0.02)(Fig.5.7). There was no
equivalent correlation with growth. Although freezing may reduce nutritional quality, all of
the frozen material sinks to the bottom and is immediately available. In contrast, fresh live
zooplankton continues to swim, is less available and may be lost with the outflow of water.
Growth, expressed as the daily growth index, was significantly different between tanks
(p<0.01). Means comparisons (Table 5.5) indicate 3 reasonably well demarcated groups. i)
Tank 11 with a poor index value of 2.5, ii) Tanks 1,3,5,6,8,12,15,16 with indices in the range
of 4.5 to 6.8 and iii) Tanks 4,9,13,14 with high index values in excess of 8.6. There were no
clear reasons for these differences, although variability in physical conditions may have been
greater than general observations suggested. The importance of frozen zooplankton to
survival was not clearly reflected in growth. Although tanks 13 and 14, which received 100%
frozen zooplankton, performed very well, tank 11 which received 99% frozen zooplankton
displayed poor growth. Feeding rate is likely to have contributed to the variability. Given the
small size of the crayfish and the absence of accurate daily biomass estimates, small
discrepancies in food quantities added may have led to significantly insufficient or excessive
feeding rates.
There was also considerable variability in growth between individuals within each tank.
Figure 5.8 illustrates the progressive increase in both size and variance (expressed as the 95%
confidence interval) of crayfish over time, in 3 of the nursery tanks. This variance is likely to
be at least partly genetically based, although nutritional and behavioural influences cannot be
discounted. In crayfish as young as 42 days, there may be as much as a 40% difference
between the smallest and largest individuals. Extrapolated to 12 months growth, this sort of
difference is extremely significant. There is clear value therefore in researching the genetic
base of such variability with the objective of selective breeding.
37
Figure 5.7. Relationship between survival and proportion of zooplankton in diet which was
frozen. Based on results of nursery growth of juvenile Cherax quadricarinatus.
Statistic
T11
T7
T12
T5
T16
T8
Tank
T1 T15
T6
T3
T14
T4
T9
T13
Daily Growth Index
2.5
4.3
4.5
4.9
5.3
6.0
6.1
6.3
6.4
6.8
8.6
9.7
9.9
10.4
65
74
75
71
70
84
67
92
65
55
68
96
56
86
Pairwise
Comparison
N
ANOVA
F = 15.1
p = 0.000
Table 5.5 Mean daily growth index (mg) statistics and ANOVA results for juvenile Cherax
quadricarinatus reared under intensive nursery conditions. Tanks 2 and 10 excluded. Means
underscored by the same line are not significantly different.
38
Figure 5.8. Mean weight (g) (horizontal line) and 95% confidence limits (vertical bar) at
weekly intervals, for juvenile C. quadricarinatus reared under intensive nursery conditions.
Graphs indicate variability in growth performance amongst tanks. Tank 11 (a), tank 9 (b) and
tank 13 (c).
5.4
Discussion:
Procedures and facilities necessary to hold broodstock, stimulate spawning, incubate eggs and
grow juveniles of C. quadricarinatus are simple and straightforward. All stages of this
operation have been successfully conducted at Walkamin Research Station, with production
success comparable to, or in excess of those documented for other freshwater crayfish species.
All procedures are advantaged by the robustness of C. quadricarinatus and the ease with
which it can be handled with no observable detriment.
Handling of broodstock required no special conditions, other than provision of water quality
of a reasonable aquaculture standard. Nevertheless, both male and female broodstock selected
for breeding purposes should be healthy and have received good nutrition prior to their
induction. Mason (1978) has indicated that the nature of nutrition obtained by the female
during ovarian maturation will influence the quality and possibly quantity of eggs produced.
Ovary staging proved to be straightforward and reliable, although its effectiveness in regard to
subsequent spawning success was not gauged. Accurate in vivo identification of mature
ovaries will be necessary to maximise synchronisation of spawning events. Recognition of
discrete macroscopic stages has been previously documented for a freshwater crayfish
(Bretonne and Avault, 1977), although an in vivo method as used in this study is apparently
new.
39
Success of spawning stimulation can be measured by the proportion of broodstock which
respond positively, and the synchrony of this response. Elevated water temperature and
increased photoperiod resulted in successful mating and subsequent egg release in 96% of
female C. quadricarinatus held, although the response was protracted over 14 weeks. By
comparison, only 22% of female Procambarus clarkii spawned under similar conditions
(Trimble and Gaude, 1988). Under more natural conditions, without artificial stimulus,
Pursiainen et al. (1983) reported that 95% of female Astacus astacus released eggs. Morrissy
(1970) indicated that 39 to 63% of C. tenuimanus spawned under natural conditions within a
normal spawning season. It is apparent that the success of stimulated spawning may depend
upon the species natural tendency to spawn and the ease with which appropriate spawning
conditions can be simulated.
Lack of synchrony in the spawning of C. quadricarinatus may indicate that the stimulus was
less than ideal. In addition, the variable period between stimulus and spawning may reflect a
varying requirement for conditioning of the ovaries to attain spawning readiness. Increased
synchrony of this conditioning period and subsequent spawning may be possible through
more accurate assessment of ovary maturity prior to induction, more finely controlled
environmental manipulations which mimic natural fluctuations on a greatly abbreviated time
scale, and possibly additional nutritional stimulus.
Equivalent mating success during the 1988 season in tanks with sex ratios ranging from 1:1 to
1:4 (M:F) indicated that pair-bonding (male-female) does not operate, other than at a
temporary level, and that increased efficiency of hatchery management can be achieved by
maintaining the proportion of male broodstock at approximately 25%. Sex ratios of this
magnitude have been successful in breeding A. astacus (Keller, 1987), Austropotamobius
pallipes (Woodlock and Reynolds, 1988) and Macrobrachium rosenbergii (Malecha, 1983).
Neither courtship nor mating behaviour were witnessed during this study, although they have
been previously described for C. quadricarinatus by Sammy (1988). It is likely that these
events took place at night when the crayfish are most active.
The incubation period for C. quadricarinatus was intermediate to those described for other
crayfish species. Bretonne and Avault (1977) indicated that the incubation of eggs for P.
clarkii may be as short as 14 to 15 days. Although increased water temperature may shorten
the incubation period (Cukerzis et al., 1979), the 66 to 72 day incubation of C.
quadricarinatus is significantly greater. By comparison, the New Zealand Parastacid crayfish
Paranephrops planifrons incubates its eggs for 16 to 17 weeks (Hopkins, 1967).
Morphological development of the eggs throughout incubation was conveniently categorised,
primarily by colour changes. Although this staging is somewhat artificial, in that the
incubatory process is entirely continuous, it does provide a useful management tool. Similar
colour and morphological development sequences have been described elsewhere (Hopkins,
1967; Malecha, 1983).
The variability in colour within each recognised stage and the inconsistent appearance in
particular of stage 2 (dark brown), are likely to be a reflection of egg quality and possibly the
nutritional state of the female during ovary maturation. Recognition of egg colours likely to
result in inferior young would be another useful management tool. Further investigation of
incubation characteristics, their causes and potential consequences, is warranted.
Attempts to incubate crayfish eggs independently of the maternal parent have been successful
40
(Mason, 1977; Nelson and Dendy, 1979), although somewhat less so than natural incubation,
in terms of proportion of eggs hatching. In addition to the poorer survival, due primarily to
fungal infections, the laboriousness of such procedures is entirely unjustified.
Fecundity estimates for C. quadricarinatus indicated that, as for other crayfish species, egg
number is a function of female size, and total fecundity is in the range of 100 to 1000 eggs per
female (Hopkins, 1967; Morrissy, 1975; Bretonne and Avault, 1977; Mason, 1977; Trimble
and Gaude, 1988; Woodlock and Reynolds, 1988b). It is clear from this literature that
considerable attrition of eggs may occur between the production of eggs in the ovary and the
release of young after incubation. Data available suggest that pleopod egg counts are 10 to
25% less than ovarian egg counts, and the number of independent young released is a further
10 to 20% less than pleopod fecundity. Given that the estimated number of young C.
quadricarinatus stocked into nursery tanks was based on pleopodal egg counts, the actual
number may have been considerably less. Survival values would consequently be higher.
Juvenile C. quadricarinatus, at the time of hatching, were approximately 0.02g and 9.5mm in
total length. Although of an adult form, quite mobile and agile, they were extremely delicate
and difficult to handle, without significant mortality. This is partly due to the increased
frequency of moulting at this size and therefore the increased likelihood of encountering soft
shelled pre- or post-moult individuals which are easily damaged. Consequently, handling of
these hatchlings should be avoided in preference to moving of the berried females prior to
release of young. This procedure was followed with great success in this study.
In 1988, berried females were transferred to release chambers within the nursery tank.
Although this method was straightforward, there was some concern that it stressed the
females, because of confinement and the difficulty of introducing food. In addition, it was
likely to have interrupted the natural post-natal relationship between mother and offspring
because the hatchlings were unable to return to the release chamber. There is considerable
information which suggests the importance of a post-natal period during which the young
become progressively independent (Mason, 1979, 1977; Bechler, 1981; Cukerzis, 1986;
Jonnson, 1987). In 1989, berried females were released freely into the nursery tanks so that
the processes of juvenile release could operate most naturally. These females were only
removed when there was no evidence of associated young.
Provision of nursery conditions in 1988 was based on the premise that juvenile C.
quadricarinatus utilized aquatic vegetation as habitat within stream environments. The
raceway tank effectively simulated the slow uni-directional flow of a small stream, and Pistia
provided ample habitat and possibly a source of nutrition. Use of a living plant within this
system was considered particularly advantageous because of: i) photosynthetic production of
oxygen, ii) stabilization of water temperature, iii) absorption of nitrogenous wastes, iv)
provision of natural food organisms associated with the plant, v) suppression of excessive
light, vi) the complexity of the root system, providing a high carrying capacity. Although the
poor production and difficulties in harvesting associated with this system do not support its
use, inclusion of living plant material in nursery systems may be worth pursuing.
The nursery facilities provided in 1989 were quite different and based primarily on the results
of a juvenile nutrition/habitat experiment (Chapt.4). The most significant characteristics were:
i) use of many small tanks (1.8mS02T) to enable batching of incoming crayfish, so that each
tank had juveniles of similar size, ii) provision of artificial substrates, iii) total feeding with
both fresh food and a formulated food. Results were considerably improved over the 1988
production and compare favourably with those documented for intensively reared juvenile
41
crayfish. Table 5.6 provides a summary of growth and survival statistics for various studies of
crayfish and M. rosenbergii. Direct comparison between results is difficult, particularly
because of the variable densities and periods employed, nevertheless it is clear that the results
for C. quadricarinatus are exceptional.
Despite the very positive result achieved, there were aspects of the strategy for which
improvements were immediately apparent, suggesting that greater productivity may be
possible. These improvements should preferably be developed through careful research rather
than simple trial and error.
The clear advantage to survival of using frozen zooplankton suggests that it should be used
exclusively. This advantage was attributable to the zooplankton being more accessible in
frozen form, because it all settles to the bottom. Live zooplankton, while having some
nutritional superiority (Eagles et al., 1984), requires considerably greater energy expenditure
to capture and is generally less accessible. Juvenile crayfish are known to have limited innate
behavioural abilities suited to food location and capture (Doroshenko, 1979; Cukerzis, 1986;
Burba, 1987). The behavioural abilities of C. quadricarinatus are possibly better suited to
benthic food materials. Thorough observational studies will be required to clarify this.
A further advantage of using frozen or possibly chilled zooplankton harvested from a pond is
that it effectively eliminates the possibility of introducing predators.
Although a range of stocking densities was employed in the nursery tanks, they were all in
excess of those generally applied in other studies (Table 6.6). There was no clear indication of
an optimal density, however, further manipulation of this parameter is worth pursuing,
particularly in regard to improved survival rates.
Similarly, habitat configuration and abundance is likely to have a significant influence on
survival. Mason (1978) demonstrated improved survival of P. leniusculus with the provision
of particular habitat. Of the two habitats provided in this study, the 'float' type appeared to be
preferred. The second 'frame' type was developed for M. rosenbergii (Smith and Sandifer,
1975) and found to be superior to several other configurations. Similar studies are justified for
C. quadricarinatus to evaluate optimal habitat requirements.
Species
Astacus astacus
Culture
Facility
Density
Period
Survival
N/m²
(days)
(%)
Growth
Range
(g)
Source
Basins
800
112
49
0.07-0.63
Keller, 1987
Cages in lake
-
126
40-52
0.02-0.59
Tamkeviciene, 1987
„
-
97
40-52
0.02-0.23
„
A. leptodactylus
„
-
90
40-52
0.02-0.35
„
A. leptodactylus
Tank
130
90
44
0.04-0.45
Koksal, 1988
A. leptodactylus
Tank
130
90
51
0.04-0.84
Basins
-
60
50
0.04-0.26
Cuellar & Coll, 1978
Tank
isolated
80
44
0.03-0.16
Celada et al. 1989
Pacifastacus
leniusculus
A. astacus
A. pallipes
P. leniusculus
42
P. leniusculus
Trough
56-80
18-60
-
Mason, 1978
Tank
130260
-
P. leniusculus
70
50
0.03-0.08
Raceway
200
100
42
0.03-1.18
Rundquist & Goldman,
1979
D'Abramo et al. 1985
P. leniusculus
Pond
20-30
120
85-90
0.03-3.34
Tcherkashina, 1977
Natural
-
120
10
0.03-2.24
„
Pond
100
90
67
0.04-0.22
Pursiainen, et al. 1983
"
Pond
300
90
32
0.04-0.17
„
"
Bin
100
90
58
0.04-0.10
„
"
Bin
300
90
50
0.04-0.08
„
Trough
30
80-90
0.02-0.5
Huner & Barr, 1984
42
70
0.10-0.75
Geddes, et al. 1988
A. leptodactylus
"
A. astacus
Procambarus clarkii
Cherax destructor
Tray
200300
263
C.destructor
Tray
154
50
40
0.02-0.65
„
Tray
770
50
30
0.05-0.45
Mitchell & Collins,
1989
„
„
Bag
880
14
92
0.02-0.10
„
Macrobrachium
rosenbergii
Cherax quadricarinatus
Pool
40
35
65-83
0.04-0.30
Mulla & Rouse, 1985
Tank
1278
36
52
0.02-0.24
This study
Table 5.6. Production statistics for rearing of juvenile crayfish (and Macrobrachium) under
various conditions. Data provided for Cherax quadricarinatus are means for 1989 production.
43
6
6.1
GROWOUT TRIALS - SUPPLEMENTAL FEEDS
Introduction:
A considerable body of information now exists on the feeding habits of freshwater crayfish.
This information indicates that the majority of species are facultative omnivores, in that they
will eat a broad range of both plant and animal materials. It is clear however, that the bulk of
ingested material is of plant origin (Lund, 1944; Capelli, 1975; Momot et al., 1978; Anon.,
1979a; Nolfi, 1980; Hessen and Skurdal, 1986; Westman et al., 1986).
Under the feeding classification of Cummins and Klug (1979), freshwater crayfish would be
considered shredders/collectors, actively grasping particles (usually plant material) from the
substrate and as necessary, breaking them into smaller particles for ingestion. It is well
established that under this method of feeding, the major nutritional benefit comes not directly
from the plant material, but from the micro-organisms (bacteria, fungi, protozoa) associated
with it (Heinle et al., 1977; Goyert and Avault, 1977, 1978; Schroeder, 1978; Chien and
Avault, 1980; Maguire, 1980; Mills and McCloud, 1983; Miltner and Avault, 1983; Avault,
1985; Day and Avault, 1986; Brunson and Taylor, 1987). This association represents
decomposition, and as a result of the processes involved, the plant material may be
sufficiently decomposed as to be termed detritus.
This generalised feeding habit is not characteristic of all crayfish. Species of Orconectes are
known to graze predominantly on living aquatic macrophytes (large plants) and may be quite
specific in their selection of plant type (Momot et al., 1978; Lodge and Lorman, 1987).
Similarly, juveniles of particular species may differ from the adults, requiring a greater
proportion of animal matter (Lund, 1944; Westman et al., 1986).
It is clear from general observations, that C. quadricarinatus is a typical detritivore,
predominantly consuming decomposing vegetable materials. Such a feeding habit is likely to
be characteristic of the genus Cherax, based on the studies of C. destructor (Anon., 1979a;
Mills and McCloud, 1983) and C. tenuimanus (Morrissy, 1979) which indicate similar
feeding preference.
Knowledge of feeding behaviour and preferred food types is fundamental to successful
cultivation of crayfish. Although a considerable amount of research has been directed at
feeding crayfish, the bulk of this information relates specifically to the culture of redswamp
crayfish, Procambarus clarkii, in the southern United States. Because of the biological
similarities of this species with C. quadricarinatus, much of the information generated has
application to the culture of the Australian species.
Unlike the development of feeds and food delivery systems for many established aquaculture
species, development of feeding technology for crayfish (specifically P. clarkii) has followed
two courses. The first is the conventional one of formulating diets from a wide variety of
materials, based upon the nutritional requirements of the species. Such diets are generally in a
pellet form and the formulation is highly species specific. The approach taken is usually to
analyse and then mimic the composition of the natural food items (Leavitt, et al., 1979;
Ostrowski-Meissner, 1987), or to mimic the composition of the animal itself. Farmanfarmaian
and Lauterio (1980) found in their study of Macrobrachium rosenbergii, that by adjusting
relative levels of essential amino-acids in their formulated feed, so that they closely
approximated those of the tail muscle, they improved growth.
The identification of specific growth-promoting substances is also essential. Fernandez et al.
44
(1983) have demonstrated that artificial diets may have to be supplemented with fresh food to
ensure provision of all essential nutrients. Lecithin, for example, is essential for the survival
of lobsters fed formulated diets (Conklin, et al., 1980). A similar requirement for specific
growth-promoting substances in crayfish has not been demonstrated, nevertheless, it is
probable.
Formulated feeds have a significant convenience advantage, however, their nutritional
adequacy and cost have worked against their general acceptance and use in crayfish
aquaculture. Feed costs for shrimp farms have been reported as high as 42% of the operating
budget (Farmanfarmainan and Lauterio, 1980) and up to 58% for catfish production (Miltner
and Avault, 1983). Initial trials feeding crayfish simply used formulated diets designed for
other species (fish and prawns) and although reasonable growth and survival were achieved,
their success was not sufficient to justify the cost (Anon., 1979b; Huner et al., 1975; Cange et
al., 1982; Morrissy, 1984; Brunson and Taylor, 1987). More recently, specific research of the
nutritional requirements of crayfish has provided better information on which formulated
diets can be based. Huner and Meyers (1979) established that P. clarkii has a protein
requirement of 20 to 30%, while Davis and Robinson (1986) and Hubbard et al. (1986) have
provided information on dietry lipid requirement and optimal protein/energy ratio
respectively. Despite this progress, a nutritionally sound and cost-effective formulated
crayfish diet has not yet been produced.
Lack of information concerning crayfish nutritional requirements and the high cost of
production of formulated diets stimulated the development of an alternative feeding strategy
in the southern United States, which aims to maximise the production of natural food
materials/organisms in the culture inclosure.
Although the developing Australian crayfish aquaculture industry, based on Cherax species,
has displayed great demand and preference for formulated feeds, the successful methods of
the redswamp crayfish farming industry may influence feeding strategies here. The use of
planted forage crops, natural vegetation, hays and other agricultural byproducts for feeding
crayfish has developed considerably. Miltner and Avault (1983) and Avault et al. (1983)
provide thorough reviews of the development of these feeding strategies.
Although many of the materials tested as potential feeds were initially suggested for
economic reasons, i.e. their low cost, it is noteworthy that they provide a food source
essentially similar to natural foods. Characteristics which appear to be of greatest importance
are the carbon:nitrogen ratio, decomposition rate and impact on water quality. Materials tested
have included Natural Aquatic Vegetation; alligator weed - Alternathera spp. (Noxious in
Australia), water primrose - Ludwigia spp., Polygonum spp. and Sagittaria; Agricultural
Byproducts; rice stubble, sweet potato leaves and vines, soybean stubble, rye hay, sorghum
hay, millet, sugar cane stalks and bagasse, tree leaves, natural grasses, corn leaves; and
Planted Forages; rice, millet and sorghum. Production of crayfish using these simple organic
materials may be further enhanced by the addition of organic or inorganic fertilizers (Rivas et
al., 1978; Rhodes and Avault, 1986; Fair and Fortner, 1981)
The advantage of planting forage crops is that they can be harvested to produce a second cash
crop. Avault et al. (1986) have suggested that the process of double-cropping has synergistic
effects whereby the cultivation of each crop actively benefits the other. Production of crayfish
(P. clarkii) has exceeded 2 tonnes/ha in forage-planted ponds (Miltner and Avault, 1983).
Although this feeding strategy has not been trialled in Australia with Cherax species, there is
considerable potential for its application. A major constraint of planted forages in the southern
45
United States has been their total decomposition prior to the crayfish achieving commercial
size. This problem would be compounded with Cherax species because of the protracted
growing season. A combined strategy involving a planted forage crop progressively
supplemented with other organic material and/or a formulated diet may prove to be the most
effective feeding regime.
Because most success in growout of C. quadricarinatus has been achieved in earthern ponds
rather than in artificial containers, definition of appropriate foods and feeding systems should
be made under pond conditions. There seems little justification in conducting comparative
supplemental feeding experiments in tanks, where the dynamic processes of decomposition
and benthic cycling cannot operate naturally. It is, afterall, these processes which are likely to
provide suitable feeding conditions for crayfish. Studies such as those of Clark et al. (1975)
on Procambarus clarkii and Fair and Fortner (1981) on Macrobrachium rosenbergii, indicate
the superiority of formula feeds over simple plant materials or fertilization, in regard to
production in tanks. It is highly likely that the results of these studies would have been
significantly different if conducted in earthern ponds where plant materials would have been
processed into a useable form by naturally present micro-organisms and fertilizers would have
had an opportunity to enhance natural productivity. It is not possible to simulate natural
decomposition processes within the confines of small artificial containers.
Growout technology for C. quadricarinatus in Australia, as applied by the existing crayfish
farming industry, is not consistent from farm to farm. Feeding practises in particular may vary
widely, primarily because of a lack of available information. A comparison of food types with
variable constituent materials and including 2 commercially available formulated crayfish
diets was therefore initiated at the Walkamin Research Station. It is clear that this study will
provide only an initial reference point, and that a considerable and specific research effort will
be required to provide effective feeding information for the culture of C. quadricarinatus.
6.2
Materials and Methods:
Six food treatments and a control were employed in a complete randomized block design with
4 replicates per treatment. Food treatments were: i) Whiskettes, a pelletised cat food (Uncle
Ben P/L), ii) Marron Pellet, prepared for C. quadricarinatus by Cheetham Rural P/L, iii)
Yabbie Pellet, prepared for Cherax destructor by Barastoc P/L, iv) Bivalve flesh, fresh
Amusium pleuronectes, v) Lucerne Pellet, 100% lucerne steam pressed (Lockyer Lucerne
Produce), vi) Potamageton, aquatic weed collected fresh from local streams. Proximate
analyses of each food are presented in Table 6.1. The control treatment received no food.
Experimental units consisted of independent rectangular enclosures within a 2000 mS02T
earthern pond. Enclosures were constructed in box-form from extruded plastic (polyethylene)
mesh (Nylex) with 6mm x 6mm mesh dimensions, sewn onto a steel frame, 1.6m x 1.4m x
1.5m high. The top was left open. Enclosures were situated in 4 rows across the pond with
approximately 1m between adjacent units. Steel stakes were driven into the pond bottom to
secure each unit. Earth from the pond floor was added to each enclosure to a depth of about
10cm.
The pond was prepared for filling by the addition of crushed limestone (CaCOS13T) at a rate
of 1tonne/ha, and inorganic fertilizer (NPK 50:20:14) at 100kg/ha. Pond filling was protracted
over several days to optimize benthic development. Organic material in the form of lucerne
hay (6 bales) was added as the pond filled. After approximately 2 weeks, planktonic
development had resulted in a Secchi reading of <50cm. At this time the pond was considered
ready for stocking. Water was added to the pond periodically to balance seepage and
46
evaporative losses.
Water within each enclosure was continuously aerated via a reticulated compressed air
supply. Crayfish habitat was provided in the form of 25cm lengths of 30mm diameter PVC
pipe.
Juvenile C. quadricarinatus were gathered from several 2000l 'nursery' tanks which had
previously been stocked with egg-bearing females. These juveniles had received regular
feeding with flake food (Frippak) and fresh zooplankton.
80 advanced juveniles were assigned to each treatment. Care was taken to select only robust
individuals in intermoult condition. Individual wet weight was measured on an electric
balance (Ohaus). Mean weights for each treatment are presented in Table 6.2. On the 19/4/89
crayfish assigned to each treatment replicate were acclimated to pond water for several hours
and then released into each enclosure.
Feeding was performed each day between 1500 and 1800hrs. Initially, feeding rate was set at
5% of body weight per day (dry weight of food). Daily body weight was estimated from the
exponential formula: Weight = 0.0495 x (X)S01.186T, where X is the age in days. This
formula was calculated using growth data from commercial growout trials (Chapt.7). 100%
survival was assumed at all times. Individual adjustments were made to this rate for each
enclosure where visual observation dictated. After day 50, feeding was reduced to every 2nd
or 3rd day.
Food
Water
Fat
Crude
Nett
Protein Protein
Ash
pH
P
Ca
Yabbie
14.0
4.0
(4.7)
23.9
(27.8)
20.4
(23.7)
7.2
(8.4)
8.3
0.84
1.38
Whiskette
9.0
8.2
(9.0)
27.9
(30.7)
22.5
(24.7)
8.1
(8.9)
5.2
1.18
1.13
Marron
12.8
1.5
(1.7)
16.9
(19.4)
14.7
(16.9)
18.4
(21.1)
7.0
1.27
4.19
Lucerne
12.6
3.4
(3.9)
16.6
(19.0)
14.3
(16.4)
8.9
(10.2)
5.9
0.40
1.23
Potamageton
95.2
0.2
(3.3)
0.7
(14.2)
0.5
(11.2)
1.2
(24.4)
-
0.19
0.97
Bivalve
86.2
0.6
(4.3)
10.3
(74.6)
6.5
(47.1)
2.8
(20.3)
6.6
1.29
1.55
Table 6.1. Proximate values (percentage) of foods used in supplemental feeding trials on
Cherax quadricarinatus. Numbers in brackets are calculated on a dry matter basis.
47
Treatment
Yabbie
Contrl
Statistic
Whisk
Marron
Bivalv
Lucern
Potam
Weight
0.51
0.47
0.44
0.46
0.35
0.39
0.39
S.E.
0.02
0.02
0.02
0.01
0.004
0.01
0.01
N
80
80
80
80
80
80
80
Table 6.2. Mean weight (g) and associated statistics for Cherax quadricarinatus assigned to
each of 7 feeding treatments.
The experiment was terminated after 96 days, at which time the pond was drained and
crayfish from each enclosure removed and weighed.
Comparison of harvest weight and survival between the 7 treatments was made using analysis
of variance. A non-parametric test (Kruskall-Wallis 1-way ANOVA) was necessary for
survival data. Pairwise comparison of means was performed with Duncan's Multiple Range
test.
6.3
Results:
Mean water temperature decreased over the period of the experiment as winter approached.
Daily minima and maxima ranged from 16 to 25.5S0oTC and 20 to 28S0oTC respectively
over the 96 day experimental period. Maximum daily water temperature less than 20S0oTC
occurred on 5 days. pH ranged from 6.9 to 9.3 with a mean of 8.1.
Survival data for the experiment are presented in Table 6.3. Survival was generally high with
the notable exception of replicate 4, and 4 other individual enclosures; replicate 2 for Control,
Lucerne and Potamageton, and replicate 3 for Bivalve.
Consistent poor survival in the 4th replicate can be attributed to the physical position of the
enclosures. This replicate was represented by the entire 4th row of enclosures which were
positioned towards the deeper end of the pond. On day 17 of the experiment, the pond was
inadvertently over-filled resulting in the partial submergence of this row only, for
approximately 6 hours. Escape by the majority of crayfish in these enclosures was confirmed
at harvest, when some 62 individuals were removed from the general pond area. These
crayfish provided an additional control group (Escape) for analyses of growth.
Poor survival in 4 additional enclosures can be attributed to predation. In each case, evidence
of either cormorant (Phalacrocorax spp.) or water rat (Hydromys spp.) predation was
observed on the plastic mesh. Capture of the majority of crayfish by the predator would have
been greatly facilitated by the confined nature of the enclosure.
Eliminating data from the 4th replicate and from the 4 enclosures subjected to predation,
survival ranged from 45 to 100%. Analysis of variance indicated no significant difference in
survival (p > 0.10) between treatments.
Growth analyses were made on all data with the exception of those from the 4th replicate and
48
with the addition of those from an 8th control group consisting of the escaped crayfish. Mean
growth for each treatment is illustrated in Fig.6.1. A 2-way analysis of variance indicated
significant variability (p = 0.06) between treatments and no significant variability in growth
between blocks (replicates). Pooling replicates, further analysis of variance indicated that the
best growth was achieved by the escape group, with less clear differences between other
treatments as depicted in Table 6.4.
No food treatment was significantly better than all others, although the Yabbie, Marron and
Whiskette pellets produced considerably better growth than the other food types.
Interestingly, the control group, receiving no added food, displayed considerable growth.
Replicate
Whisk
Marron
Yabbie
Contrl
Bivalv
Lucer
Potam
1
2
3
4
60
95
75
10
55
45
80
0
55
85
60
25
75
5
65
10
85
90
0
5
85
5
100
70
90
5
85
10
Adjusted
Mean
77
60
67
70
88
93
88
Table 6.3. Percentage survival of Cherax quadricarinatus in a supplemental feeding trial.
Adjusted mean is the mean survival calculated, eliminating replicate 4 entirely, replicate 2 for
Control, Lucerne and Potamageton and replicate 3 for Bivalve (see text).
49
Figure 6.1. Mean weight (g) of Cherax quadricarinatus after 96 days subjected to 8
supplemental feeding treatments. See text for treatment details.
Weight
Potam
Contrl
Lucern
Bivalv
Whisk
Marron
Yabbie
Escap
9.6
10.3
10.6
11.5
12.7
13.4
13.8
16.3
0.55
0.82
0.65
0.80
0.68
0.97
0.84
0.82
36
29
38
36
46
36
40
62
Pairwise Comparison
S.E.
N
ANOVA
F = 12.7
p < 0.001
Table 6.4. Mean weight (g) and analysis of variance results for Cherax quadricarinatus after
96 days subjected to 8 supplemental feeding treatments. Means underscored by the same line
are not significantly different (p < 0.05).
6.4
Discussion:
Despite the lack of statistical significance in all cases, it was clear that the formulated feeds
produced better growth than the more simple food types. A longer experimental period or
higher mean water temperature would have resulted in greater growth and possibly more
significant differences between the feed types.
The exceptional growth of the escaped crayfish, which received no supplemental feeding, is
likely to have been a density effect. Although subjected to greater predatory pressure resulting
in poor survival, the escaped group represented a density less than 1/20mS02T. Because the
pond was initially prepared with both organic and inorganic fertilization, there was sufficient
food in the general pond area to support excellent growth. This food would have been detrital,
as no macrophytes developed over the experimental period. By comparison, the control group
within the enclosures displayed significantly less, although still considerable growth. Based
upon growth performance in other trials (Chapt.7), projected growth of the control group after
365 days would be in excess of 50g (individual weight), and equivalent to a yield greater than
3,000 kg/ha.
The growth of crayfish provided with bivalve flesh (47% protein) was not significantly
different to that with lucerne (16% protein), or the control group (no added protein). This
would suggest that the benthic detritus and associated micro-organisms provided adequate
nutrition, including protein. Superior growth on the Yabbie, Marron and Whiskette pellets is
likely to be attributable to more subtle food characteristics, such as specific amino-acid
balance and/or mineral/vitamin constituents.
Although poorest growth was displayed by the group receiving Potamageton weed, it was not
statistically less than the control, lucerne or bivalve groups. Potamageton was clearly
50
consumed vigorously, and has been used effectively as a maintenance diet for tank held
crayfish (Chapt.5). Nevertheless, it does not provide sufficient nutrition in association with
benthic detritus, to achieve maximal growth.
The 3 formulated diets trialled were essentially similar in proximate composition to the diet
formulated by Huner et al. (1974), which proved suitable to 17 species of freshwater crayfish.
Although the 3 diets differed to some extent in their proximate composition, growth of
crayfish fed each was similar. It is likely that relative deficiencies in these diets may have
been overcome by the availability of nutrients in the natural detritus on the pond floor. This
supports the authors opinion that pond production is more effective than tank production
where natural detritus is not available.
The results of this study echo those of similar trials for other crayfish species which have
indicated that good survival and growth can be achieved on formulated diets. However, the
cost-effectiveness of using these diets at a commercial scale, when reasonable growth rates
can be achieved using less costly materials, is not certain. It may be most effective to combine
the use of a formulated diet with less costly food materials and thorough pond preparation,
which maximises benthic productivity. Based upon the results generated, it would appear that
the planting of forage crops, as practised in the culture of red swamp crayfish (Procambarus
clarkii), may be very effective.
A suitable formulated diet for C. quadricarinatus is yet to be defined, however, its application
has great potential if designed as a supplementary feed for pond growout. As such it should be
composed of locally available materials which provide a protein level in the order of 20%, not
necessarily animal protein, and with some effort made to approximate the amino-acid balance
characteristic of the muscle tissue of the crayfish (Chapt.8). Mineral and vitamin content may
be adjusted to allow for any potential deficiency of the pond substrate. The bulk of the diet
may be most effectively composed of coarse plant material with low C:N ratio such that it
will provide a good substrate for decomposition and be of a particle size suitable to be located
and manipulated by the crayfish. It should be sufficiently stabile to sink through 1-2 metres of
water intact, and then break open within 24hrs. Clearly, there will be many other
factors/ingredients of importance in the formulation of an ideal C. quadricarinatus food.
Nevertheless, there is now sufficient information to produce a reasonable prototype.
Future feeding research should concentrate on pond preparation (maximisation of benthic
productivity), characteristics and suitability of planted forage crops and relative value of
variable levels of supplementary formulated feeds.
51
7
7.1
GROWOUT TRIALS - COMMERCIAL PRODUCTION
Introduction:
Production of freshwater crayfish is significant in the United States, Europe (including
Britain) and more recently, Australia. In all cases, the production base historically has been
from wild fisheries, which may be very extensive. In Louisiana, for example, wild harvests of
Procambarus clarkii may exceed 30,000 tonnes per annum (Huner, 1988a). Similarly, in
Australia wild fisheries for Cherax destructor and C. tenuimanus pre-dated cultivation. In
contrast, however, a wild fishery for C. quadricarinatus has not developed, despite its large
size, culinary appeal and its suitability for aquaculture. The remote distribution of this species
(Chapt.1) has been primarily responsible for the 'lack of interest', however, with commercial
aquaculture now successfully demonstrated, exploitation of wild stocks (for collection of
broodstock) is likely to increase.
Cultivation of crayfish dates back at least some 20-30 years and involves widely varying
practices in different regions. Because of the industry's size, the farming of redswamp
crayfish in the southern United States is perhaps the most publicised. This industry is
characterised by extensive methods, generally involving large (8-20ha), shallow ponds and
double-cropping with forage crops. These methods have to some extent been transplaced to
parts of Africa and Spain (Karlsson, 1977) where Procambarus has been introduced.
In Europe, cultivation of crayfish was stimulated with the decline of natural stocks caused by
crayfish plague. Plague-resistant species (Pacifastacus leniusculus and others) were
introduced from North America, particularly during the 1960's, to alleviate reduced wild
production, however, cultivation practices also began to develop. Methods employed are
usually more intensive than in the southern U.S., with a considerable proportion of effort
expended on hatcheries and juvenile rearing (Huner and Lindqvist, 1987, Huner, 1988b).
Most juveniles are stocked into natural waters, although increasing attention is being paid to
culture ponds. These ponds are generally 40m by 7m and up to 2m deep. Water is flushed
through the ponds and attention paid to maintenance of water quality, however, supplemental
food is usually not provided. Culture of P. leniusculus in Britain similarly involves stocking
of artificially reared juveniles into small-medium sized farm ponds (Richards and Fuke, 1977,
Richards, 1983). There is little or no feeding and minimum on-going maintenance over a
grow-out period of 2-3 years.
By comparison, farming of crayfish in Australia is developing its own unique characteristics.
A considerable body of information on culture practices has been documented (Morrissy,
1970b, 1976a, 1976b, 1980, 1983; Anon., 1973, 1977, 1979b, 1981, 1984a, 1989; Johnson,
1978a, 1978b, 1983; Bishop, 1980, 1989; Carroll, 1980a, 1980b, 1981; Crook, 1980, Mills,
1980, 1983, 1989; McLaren, 1980; Campbell, 1983; Bennisson, 1984; Owen and Bowden,
1986; Hutchings, 1987, 1988), although much of this is of an anecdotal nature or is not widely
available. To a degree, this is a reflection of the industry's early development status, where
much of the technology applied is localised and inconsistent, and commercially unproven.
Culture of yabbies {C. destructor) and marron (C. tenuimanus) first began some 10 to 15
years ago, although commercial success has been elusive (Chapt.1). Cultivation of C.
quadricarinatus began 4-5 years ago and is already achieving some commercial success.
The culture technique generally employed for Cherax species in Australia involves
rectangular, earthem growout ponds, from 500m2 to greater than 1ha, and 1 to 2m deep.
Juvenile crayfish are provided either from a hatchery where mature female and male crayfish
are held in tanks under semi-controlled conditions, or from broodstock ponds in which a
52
reproducing population is held (see Chapt.5). The latter is particularly prevalent in the
aquaculture of C. quadricarinatus. Juveniles of 0.1 to 2.Og are taken from the hatchery tanks
or broodstock ponds and stocked into the growout ponds at densities of between 2 and 10/m2
and grown out to commercial size over a period of between 1 and 3 years. Feeding varies in
intensity, but usually includes some fresh vegetation or agricultural by-product and some
pelleted ration, most often of the 'chicken pellet' type. Artificial shelter may also be provided
in the form of lengths of pipe, beer cans, car tyres or extraneous roofing materials. Aeration is
often provided by mechanical agitators. Although some culling may occur throughout the
growout period, once the bulk of the crop has achieved commercial size, it is totally harvested
by trapping and/or drain harvesting.
There has been some attention paid to semi-intensive tank growout of C. destructor (Mitchell
and Collins, 1989), although its commercial application has not been successful. As in the
aquaculture of all species, there is also a small proportion of interest in super-intensive/battery
culture of freshwater crayfish. The advantages of this type of culture are well documented
(Goyert and Avault, 1978; Molfi, 1980; Conklin and Chang, 1983; Davis and Robinson,
1986), however, successful commercial systems have yet to be developed. Results of trials
such as those of Kowarsky et al. (1984) and Morrissy (1984) indicate that Cherax species,
under highly intensive conditions, perform considerably better when given access to a detrital
food base. It would seem quite futile to simulate such conditions artificially, when they occur
most effectively under natural conditions in earthern ponds. Nevertheless, the 'intensive
fraternity' will continue their quest and perhaps achieve some level of success in the future
when crayfish nutrition is better understood.
Production figures for crayfish are widely documented and may indicate natural or managed
(cultivated) production. These figures are not always directly comparable as they represent
different types of production. Under managed systems, production may be defined as total
biomass harvested, whereas under natural conditions it usually relates to increase in biomass
over a given time or sustainable yield from fishing. Clearly, natural systems cannot be totally
harvested, but managed systems can, because provision is made for restocking. Natural
production figures presented in Table 7.1 give a reference point against which the
effectiveness of managed production can be gauged. The most productive systems, culturing
Procambarus and Cherax, achieve yields in the order of 500 to 2000 kg/ha.
In assessing the aquaculture potential of C. quadricarinatus, commercial-scale production
trials were planned. In the first instance, techniques typical of Cherax culture elsewhere in
Australia were considered appropriate with some modifications stimulated by specific
biological attributes of C. quadricarinatus. One attribute in particular which warranted further
attention was C. quadricarinatus' response to water current (Chapt.2). There were obvious
implications in regard to harvesting techniques which have received on-going investigation.
Crayfish
Country
Production Type
Yield(kg/ha)
Source
Cherax
Australia
NaturalManaged
Mitchell and
Collins, 1989
Procambarus
USA
NaturalManaged
Orconectes
North America
NaturalManaged
100-200mean
500-1000max
<2000
200-600mean
1000-2000max
<3000
150-600none
Huner, 1988
Momot, 1988
53
Orconectes
Pacifastacus
EuropeIntroduced NaturalManaged
USA
NaturalManaged
Pacifastacus
Europe
Astacus
leptodactylus
Turkey
300-500none
< 100none
NaturalManaged none10,000?500100
Natural
< 100
Momot, 1988
Lowery and
Holdich, 1988
Karlsson,
1977Lowery
and Holdich,
1988
Koksal, 1988
Table 7.1. Production statistics for freshwater crayfish throughout the world. This list is not
exhaustive, but includes the most significant productions. Natural and managed productions
are not directly comparable as explained in the text.
7.2
Materials and Methods:
Commercial scale production trials were initiated in the summer of 1988/1989 and again in
1989/1990. Materials and methods described apply to the first trial. Modifications to these
techniques for the second trial are described after.
Three earthern ponds were allocated to production trials for C. quadricarinatus. They were
similar in all respects, with length of 45m, width 25m, 1.2m deep at water inlet and 1.8m deep
at water outlet. Pond surface area was 1200m2 (0.12ha). Internal batters were 2:1. The water
inlet consisted of a 15cm diameter PVC pipe extending 2m into the pond and supported by a
wooden jetty. A concrete slab beneath the pipe prevented erosion during filling. A 20cm
diameter concrete gutter ran the length of the pond from the inlet to a concrete monk at the
ponds deepest point. A 15cm diameter PVC outlet pipe extended from the monk, through the
bund wall to a concrete harvest box, 1.5m by 2.0m by 0.6m deep. Inlet and outlet water flow
was controlled by gate valves at each end of the pond. Each pond was lined with 30cm of
impervious clay, however, due to their age, considerable seepage occurred.
Each pond was individually equipped with a Hardiplank (James Hardie) perimeter fence,
30cm high, installed on the pond edge to minimise crayfish escape. The ponds were also
individually enclosed within a tent of 25mm nylon mesh to minimise bird predation. Potential
water-rat (Hydromys spp.) predation was countered by setting Elliot mammal traps.
Prior to pond filling, volunteer vegetation was cut back at ground level and removed. Crushed
limestone (CaCOa) was applied at 1000kg/ha and inorganic fertilizer (NPK 50:20:14) at
100kg/ha. Organic fertilizer was also added in the form of baled lucerne hay, 5 bales/pond.
Crayfish habitat was provided by securing a 30cm wide strip of plastic mesh (Rheem
Multimesh) to the pond bottom. This mesh floats up off the bottom creating artificial weed. 6
strips of mesh were installed in each pond.
Ponds were filled some 2 weeks prior to the desired stocking date. Over this period, water
quality parameters (max/min temperature, pH, dissolved oxygen) were measured daily.
Juvenile crayfish were stocked in December 1988 (Table 7.2). Pond 1 recieved juveniles
reared in a raceway (Chapt.6), while ponds 2 and 3 were stocked with female crayfish bearing
late stage eggs. After hatching and release of young, these females were removed. Stocking
numbers were based on fecundity estimates. Recording of water quality parameters was
54
initiated when feeding began in February 1989 and was maintained at a frequency of 2 to 3
times per week.
Food provided consisted primarily of composted lucerne chaff, replaced by lucerne pellets
after the 12/4/89, and secondarily of marron pellets (Cheetham Rural) and whole sorghum
seed. Food was broadcast over the pond surface every 2-4 days. The feeding regime is
summarised in Table 7.3.
Pond
Date
Stocking
Method
Number
Stocked
Density
no./m²
Mean Size
(g)
1
2
7/12/88
11/12/88
6,000
13,345
5
11.1
0.07
0.02
3
11/12/88
Juvenile
Berried
Female
Berried
Female
11,166
9.3
0.02
Table 7.2. Statistics for stocking of juvenile Cherax quadricarinatus into growout ponds for
commercial production trials, 1988/1989.
Month
Dec 1988
Jan 1989
Feb
Mar
Apr
May
Jun
Jul
Aug
Total
Lucernekg/feed
not fed
not fed
3.5
3.5
5.0
6.0
6.0
6.0
6.0
170.5kg
n
Marron Pellet
kg/feed
n
Sorghum
kg/feed
n
4
7
6
4
5
5
3
3.5
6.0
6.0
6.0
55.0kg
2
4
2
2
-
3.5
6.0
6.0
6.0
6.0
61.0kg
2
4
2
2
1
Table 7.3. Feeding regime for commercial production trial of Cherax quadricarinatus. Food
weight refers to quantity provided to each pond, n times over each month. Total represents the
total quantity of food of each type provided to each pond during the growout period.
Periodic sampling of crayfish from each pond was conducted to provide estimates of growth.
Population estimates were made using the Petersen estimate (Begon, 1979). r individuals are
captured, marked and released back into the population. A second sample (n) is captured
some days later of which m are marked. The population size N can then be estimated, where
N = rn/m. For this study, groups of crayfish were marked with white finger-nail paint.
The process of sampling also provided an opportunity to test various flow trap configurations.
Although such testing was interpretive and evolved according to progressive results, the
55
information recorded did provide for some semi-quantitative analysis. Flow trap designs were
either fully submerged or of a box and ramp type. Parameters tested included flow rate, water
source and supplemental attractants. In addition, other harvesting methods were considered. A
portable cage for drain-harvesting was tested.
A second production trial was initiated in the summer of 1989/90. The same ponds were used
with similar preparation and maintenance. Modifications over the first trial included the
provision of a considerably greater quantity of organic material in the form of mulching hay.
This strategy was employed on the basis of its success in the culture of redswamp crayfish in
the southern United States. Hay was spread across the pond bottom after liming and inorganic
fertilization, at a rate of 0.5 to 1.0 kg/m2. Ponds were filled 2-4 weeks prior to stocking
during which time dissolved oxygen (DO) levels remained below 1ppm despite flushing and
aeration. Stocking took place after the DO levels had climbed above 4ppm (early morning).
A second modification to the production strategy was the use of advanced juveniles for pond
stocking. These juveniles, 0.1 to 0.5g wet weight, were the product of stimulated winter
spawning (Chapt.6). A third alteration related to the stocking date. Seasonal water
temperature fluctuations at Walkamin see optimal conditions returning after winter by late
September. Advanced juveniles were stocked as they became available from mid-October
through to mid-November. Stocking details are summarised in Table 7.4. Results of this trial
were not available at the time of writing this report.
Pond
1
2
3
Date
Number
Stocked
Density
no./m²
Mean Size
(g)
13/10/89 - 23/10/89
27/10/89 - 14/11/89
15/11/89 - 16/11/89
6,476
7,717
2,535
5.4
6.4
2.1
0.25
0.21
0.23
Table 7.4. Statistics for stocking of juvenile Cherax quadricarinatus into growout ponds for
commercial production trials, 1989/1990.
7.3
Results:
Management of water quality during the growout period posed no significant problems.
Dissolved oxygen levels were consistently high (>5ppm) at all times. Although mechanical
aerators were not used, new water added to balance seepage and evaporative losses was
sprayed onto the pond under pressure, thus providing considerable aeration. In addition, all
ponds were orientated to maximise exposure to prevailing wind.
Water temperature declined over the growout period to June (Fig.7.1), as autumn and winter
progressed. Daily fluctuations were in the order of 3 to 4°C. Mean maximum temperature
ranged from 20.0 to 35.0°C and mean minimum from 16.0 to 29.5°C.
pH fluctuations were consistent between ponds and were therefore pooled for presentation of
statistics (Fig.7.1). pH remained within 'healthy water' limits, ranging from 6.7 to 9.7 over the
growout period. Monthly means indicate a reasonably high pH after pond filling due the
effects of liming and fertilization, followed by a decreasing trend through to May. This is
likely to be a reflection of decreasing productivity in the water due to decreasing temperature
and heavy flushing as described below. A sharp rise occurred from June through August as a
spring bloom of phytoplankton occurred.
56
Figure 7.1. Mean water temperature and pH fluctuations in commercial production trial
ponds. Monthly means are derived from readings every 2-4 days.
A potentially hazardous blue-green algal bloom (Anabaena airmails) occurred in all ponds at
the end of February. It was controlled by flushing ponds with fresh water at a rate of
approximately 20% per day, over several days. Although its development remained in check,
the blue-green algae persisted for some months before disappearing. Development of a
filamentous green alga in pond 3 in early June could not be controlled and led to the ponds
draining and harvesting to avoid potential water quality problems. Although aquatic
herbicides were available, their impact on crayfish is unknown and they were not used.
Estimates of growth and population size over the growout period are presented in Fig.7.2 and
Table 7.5 respectively. In both instances it was clear that estimates were not particularly
accurate. Although growth estimates were based on samples in excess of 100, they appear to
have been significantly biased towards larger individuals. It is likely that the sampling
technique, flow-trapping, did not provide representative samples, due to size specific
behavioural factors. These are discussed below.
Despite the inaccuracy of growth estimates, it was clear that growth was significantly
depressed after the first 100-150 days. This growth depression corresponds to the reduction in
water temperature to sub-optimal levels after April (Fig.7.1)(Chapt.2). A projected growth
curve is presented in Fig.7.2 to represent actual growth likely under the prevailing conditions
and allowing for increasing temperature after winter (A). A second projected growth curve
(B) represents potential growth if advanced juveniles (0.2 to 0.5g) were stocked at the
beginning of summer (September). This is the strategy employed for the current 1989/90
production trial.
Population estimates were also inaccurate as indicated by the wide confidence intervals and
poor reflection of actual numbers at harvest (Table 7.5). Numbers marked in the markrecapture studies are likely to have been too small.
Production figures presented in Table 7.6 indicate that the production strategy employed and
C. quadricarinatus' response to it, were successful. Despite reasonably poor survival, the yield
57
was in excess of 1200kg/ha in each pond at harvest. The high survival (74%) in pond 1 may
be attributed to the lower stocking density, but more particularly to the increased mean size of
juveniles at stocking. The growth figures presented previously (Fig.7.2) indicate that the bulk
of biomass increase occurred during the first 4 months, when water temperature was most
conducive to good growth. Although all ponds were harvested prior to the majority of
crayfish achieving a commercially acceptable size, projected yields for 12 months growth
suggest that culture of C. quadricarinatus is extremely viable.
The feeding regime employed was successful from the point of view that good growth and
total production were achieved, and excess food was not apparent. By estimating progressive
biomass a notional daily feeding rate was calculated (Table 7.7). Although several levels of
estimation are involved, which compound the error factor, the analysis indicates that a feeding
rate equivalent to 1-4% of biomass/day was employed.
Fig. 7.2. Growth estimates based on sampling of the population during commercial
production trials for Cherax quadricarinatus. Terminal weights are based on representative
samples after harvest. Projected growth curves represent estimated actual growth, under actual
conditions (A) and for early summer stocking of advanced juveniles (B).
Pond Period Elapsed Marked N Population Estimate
95% C.I.
Harvested
n
lower upper
1
1
1
58
114
153
247
100
134
933
3,136
715 1,151
2,165 4,106
4,441
2
2
2
108
149
265
230
200
3
3
3
109
145
187
271
200
3,373
3,185
2,028 4,718
3,038 3,331
7,200
2,032
3,550
1,377 2,687
1,643 5,457
4,538
Table 7.5. Population estimates for growout ponds in commercial production trials of Cherax
quadricarinatus, based upon Petersen mark-recapture methods. Actual harvested number is
presented for comparison.
Stocked
Harvest
Yield
Pond
Date
N
Density
no./m²
Date
Period
days
N
Density
no./m²
Survival
%
Size
g
Biomass
kg
Actual
kg/ha
Projected
kg/ha
1
7/12/88
6,000
5
11/8/89
247
4,441
3.7
74
34.3
152
1,267
1,826
2
11/12/88
13,345
11.1
2/9/89
265
7,200
6.0
54
32.0
231
1,925
2.667
3
11/12/88
11,166
9.3
16/6/89
187
4,538
3.8
41
35.9
165
1,375
2,667
Table 7.6. Production figures from commercial production trials for Cherax quadricarinatus.
Projected yields represent estimates for 12 months growth.
Month
Biomass
(kg)
Food Quantity
(kg)
Feeding Rate
(%)
Feb
Mar
Apr
May
Jun
Jul
Aug
40
60
80
100
120
140
150
28
75
54
36
42
54
30
Mean
2.3
4.2
2.3
1.2
1.2
1.3
0.7
1.9
Table 7.7. Estimated daily feeding rate for Cherax quadricarinatus in commercial production
trials. Feeding rate is expressed as percentage of crayfish biomass. Food includes all food
types.
Predation of crayfish by water rats (Hydromys species) became significant on some
occasions. Their activity was irregular and characterised by long periods (several weeks) of
no observed activity, followed by intense predation in all ponds. 2 to 3 successive nights of
intense predation resulted in the loss of over 100 crayfish. Constant trapping and destruction
of preferred habitat adjacent to the ponds appears to be an effective management strategy.
Electrified perimeter fences have been used with great success by the aquaculture industry to
minimise rat predation. Bird predation was effectively eliminated by the mesh cover. Other
predators were not observed.
59
Use of flow traps for sampling resulted in considerable development in trap design. The 2
basic trap configurations developed were submerged, and box and ramp traps, illustrated
diagrammatically in Fig.7.3 and 7.4. The submerged trap operates by providing a typical
funnel entrance directly opposite to a concentrated stream of water within the trap. Crayfish
responding to the flow move through the entrance and are captured. Water is supplied to the
trap by a flexible hose and the trap is positioned on the pond bottom, fully submerged. Box
and ramp traps consist of an enclosed box containing and supplied with water (Fig.7.4), to
which a ramp is connected directing overflowing water to the ground. Crayfish detecting the
flow from the ramp move up it and are then captured in the box. This trap is positioned on the
pond edge in 20-30cm of water, or entirely out of water during drain harvesting. A ramp
consisting of a pipe is most effective, as it concentrates the water current.
Quantification of the relative effectiveness of these flow traps was made difficult by the
variability of conditions under which they were deployed. It was clear however, that the flow
traps were an order of magnitude more effective than baited traps. Under ideal conditions of
high crayfish density, best bait (chicken offal) and dark nights, baited traps captured between
10 and 20 crayfish. By comparison, both flow traps under similarly ideal conditions, caught
on average 100 to 200, and up to 1000 crayfish.
Other characteristics gleaned from flow-trapping experience were that the catch was generally
biased towards larger individuals, water supplied to the traps from a foreign source produced
increased catch rates in comparison to use of water from the pond being sampled, and a flow
rate of approximately 301/min was more effective than either 201/min and 401/min. The
addition of supplemental attractants (bait) had no discernable effect, suggesting that that
response is not related to feeding.
Fig.7.3. 'Submerged' flow trap used for the capture of Cherax quadricarinatus. Side view (a)
and plan (b). Trap generally constructed as steel frame covered in fine mesh (shadecloth).
60
Fig.7.4. 'Box and Ramp' flow trap used for the capture of Cherax quadricarinatus. Constructed
from various materials.
Drain harvesting of C. quadricarinatus ponds (including several broodstock ponds) was
performed on 8 occasions. Under the varying conditions prevailing on these occasions,
patterns of some significance became apparent. When a pond was drained quickly with no
extraneous introduction of water, the crayfish moved with the water and were flushed out
through the outlet pipe. To maximise the efficiency of this for harvesting of the growout
ponds, a steel-mesh box was constructed to fit into the harvest box on the outside of the pond.
Once the 'crop' was flushed into this mesh box, it was lifted by tractor and removed. In
contrast however, if a small flow of water into the pond was maintained while the pond was
drained, crayfish moved with the draining water until it was all but gone, and then moved
upstream into the water flow. This effectively concentrated the crayfish and provided an ideal
opportunity to deploy the box and ramp trap, which operated with great success.
7.4
7.4.1
Discussion:
Production:
The production of crayfish achieved in the first growout trial at Walkamin was commercially
acceptable and confirms the aquaculture potential of C. quadricarinatus. Yields were directly
comparable to the best achieved for Cherax culture elsewhere in Australia and for
Procambarus culture in the United States (Collins and Mitchell, 1989). They were
considerably better than those of many other species of freshwater crayfish (Holdich and
Lowery, 1988).
Direct extrapolation of the yields achieved to large-scale commercial operations is not
unreasonable, however, considerable refinement of the production strategy is likely and
improved yields in excess of 2,000 kg/ha are realistic.
A second growout trial of C. quadricarinatus at Walkamin Research Station currently
underway, has involved some modifications which were immediately suggested by the first
61
trial. These are: i) stocking of advance juveniles rather than newly hatched crayfish, ii)
stocking as near as possible to the onset of optimal temperature conditions in spring, iii) a
uniformly lower stocking density of between 3 and 7 per square metre.
The stocking of advanced juveniles in spring was made possible by stimulating 'winter'
spawning of captive broodstock and then intensively rearing juveniles under controlled
conditions with provision of a superior diet of zooplankton and formulated feed, and in the
absence of predators. These procedures constitute the subject of Chapt.6. The advantages of
this approach are considerable. Of major significance is the maximisation of optimal
temperature conditions while the crayfish are in their fastest growth phase and prior to the
onset of maturity and its associated energy costs. Although 12 months (including winter) of
growth may still be necessary to achieve a commercially acceptable size, it is likely that the
greater the length of the first summer period, the greater will be the growth and therefore
production achieved.
Definition of optimal stocking density is dependent upon size at stocking, feeding regime,
target harvest size and general management strategy. It would appear from this study that
around 5/m2 may be most efficient, although studies of Procambarus clarkii and
Macrobrachium rosenbergii have indicated that a density of 2/m2 was most profitable (Lutz
and Welters, 1986; Karplus et al., 1986). Avault et al. (1975) have suggested that overcrowding causes stunted growth resulting in the entire crop being commercially unacceptable.
The passive nature of C. quadricarinatus, may enable it to perform well under higher densities
than more aggressive species. Under the culture strategy presently employed, it may not be
economically efficient to go beyond 5/m2, however, with improved knowledge of food and
feeding rates, an effective increase may be possible.
The notion of fixed stocking density for the entire growout period is an accepted one.
Increased efficiency of culture may be achieved by managing biomass rather than numerical
density, however, the labour and energy costs of periodic culling to maintain a desired and
constant biomass are likely to be prohibitive. Nevertheless, some periodic sampling of the
'crop' is a desirable management exercise to ensure that stock are healthy and performing as
expected. The method of sampling is unimportant providing that a truly representative sample
is obtained. In this regard, the flow traps (as discussed below) may not be ideal, as they
appear to produce a biased sample. Moreover, they necessitate active movement by the
crayfish and therefore are less representative of unhealthy or otherwise less mobile
individuals. Seining or removal of artificial habitat structures may be more effective.
Estimates of population size, which in turn enable estimation of standing biomass, mortality
since stocking and production, usually involve mark/recapture procedures. The methods are
quite straightforward and have been used regularly for crayfish (Abrahamsson, 1966; Brewis,
1979; Price and Payne, 1979, 1984), however, as the estimates made in this study
demonstrated, the number of marked individuals must be sufficient to enable an accurate
estimation. Begon (1979) provided tables of sample sizes required to achieve particular levels
of accuracy for different sized populations. In general however, the number of marked
individuals and subsequent sample size should be in the order of 10% of the total anticipated
population. More complex methods of population estimation have been suggested, such as
that of Morrissy and Caputi (1981) formulated specifically for marron. Despite being less
'user friendly1, these methods have great application, although they may have to be
formulated specifically for species cultured and localised culture conditions.
62
7.4.2
Food/Feeding:
A considerable discussion of food and feeding methods appropriate to crayfish was provided
in the introduction to this chapter. As was pointed out, the importance of detritus in the
crayfish diet is unquestionable. From this point of view, the feeding regime applied in this
study was appropriate. The bulk of food provided (mostly lucerne) would have 'fed' the pond
sediment and its associated fauna/flora of micro-organisms, which in turn provided food for
the crayfish. As this was the first commercial-scale crop of crayfish grown at Walkamin, it is
difficult to draw
conclusions on the relative effectiveness of the feeding strategy. Clearly, successful
production is a mark of suitable feeding, however, greater success is possible with improved
feeding methods.
Lucerne would appear to be a suitable base diet. It has sound nutritional qualities, is relatively
low in heavy structural material and decomposes quickly and efficiently. Nevertheless, the
superior attributes of rice and forage sorghum identified by various researchers in the
southern United States (Chien and Avault, 1979, 1980, 1983; Rivas et al., 1978; Avault et al.,
1983; Miltner and Avault, 1983; Rhodes and Avault, 1986; Brunson and Taylor, 1987;
Brunson and Griffin, 1988), suggest that these materials should be trialled with C.
quadricarinatus.
Use of these various crops necessitates consideration of residual pesticides. Unfortunately,
common agricultural practises applied to the cultivation of forage or grain crops includes
application of pesticides likely to be lethal to crayfish. A considerable body of information on
acute toxicity of various pesticides has been documented for Procambarus clarkii (Muncy and
Oliver, 1963; Cheah et al., 1979, 1980; Ekanem et al., 1983; Huner and Barr, 1984) which
may be applicable to C. quadricarinatus. Nevertheless, due to the likelihood of adverse sublethal effects, it would be most desirable to use food material free of pesticide residues.
Method of application of the forage crop material may be in the form of hay, chaff or pellets.
Hay and chaff require some period of composting to be most effective. The increased specific
gravity of pellets which permits them to sink in water is certainly more convenient. In
addition, pelletising provides an opportunity to supplement other materials as required.
There is no doubt that the convenience of pelleted food and the low cost in particular of
chicken pellets, has led to their popularity in crayfish farming. It is equally clear that these
two advantages represent the only reasons to use chicken pellets, as they are nutritionally
inadequate and detrimental to water quality. Much of a chicken pellets composition is derived
from crushed grain which is unacceptable to the crayfish and slow to decompose. Similarly, a
relatively high proportion consists of 'fines', tiny particles which remain in suspension when
introduced to water, feeding bacteria, consuming oxygen and reducing water quality.
Exclusive feeding of crayfish ponds with chicken pellets has been observed to cause a
significant excess of organic material, and therefore presumed increased BOD, stressful
conditions and reduced production and profitability. The pellet form is the only characteristic
that crayfish and chicken pellets should have in common.
Some of the pelleted rations now available for crayfish, are loosely based on chicken pellet
formulae, and are therefore not ideal. The companies involved have limited access to
appropriate nutritional information on which to base their formulations, and cannot be held
responsible. It is hoped that sufficient nutritional information will soon be available to enable
formulation of more appropriate crayfish rations. In the mean time, the use of a variety of
63
feeds, such as that applied in this study, may be more effective than a single food material.
The diet may include formulated feeds (prawn, fish or crayfish pellets) used sparingly and
should be characterised by materials which i) decompose relatively quickly, ii) do not
dissolve readily, iii) do not cause adverse water quality conditions and iv) are cost effective.
7.4.3
Economics:
An economic assessment of the productivity of C. quadricarinatus culture has not been made.
The variability of techniques applied in the existing industry would make any economic
evaluation too simplistic. Nevertheless, economic studies for other crayfish farming industries
do provide a reference point for comparison. Both the crayfish (Procambarus clarkii & P.
acutus acutus) farming industry of Louisiana and the yabbie (Cherax destructor) farming
industry of southern Australia have been the subject of detailed economic studies
(Dellenbarger et al., 1987; Dellenbarger and Luzar, 1988; Staniford and Kuznecovs, 1988;
Staniford, 1988). Although these two industries differ markedly in technology, a common
theme was the uncertainty of yields and price, and the inherent risk therefore involved.
Stanifords (1988) proposed economic model for yabbie farming incorporated an anticipated
variability in yield of 2,000 to 3,800 kg/ha/annum and in price of $8.00 to $12.00 /kg. Yields
of this magnitude are potentially possible for C. quadricarinatus, although they are somewhat
higher than those achieved in this study. Price for C. quadricarinatus is extremely variable,
but considerably greater than that proposed for yabbies. Assuming that the production
strategy (and its costs) proposed for yabbie culture is similar to that which develops for C.
quadricarinatus, the conclusions reached by Staniford (1988) may apply to the culture of this
species. The conclusion drawn was that, although potentially profitable, crayfish farming was
a risky investment.
Staniford and Kuznecovs (1988) demonstrated increased profitability as farm size increased
from 5 to 20 hectares. Economically successful farming of C. quadricarinatus may necessitate
large hectarage, like that characteristic of crayfish farming in the southern United States.
7.4.4
Intensive Culture:
Simplified economic assessments have led many prospective crayfish farmers to consider the
development of super-intensive, battery-style culture practises. These are generally
characterised by stocking densities in excess of 25/m2. In theory, intensive systems may
appear very productive, however, their commercial reality for growout has not yet been
established for any decapod crustacean species. Application of intensive technology to
hatchery or nursery phases of aquaculture is of course well documented, and likely to become
an integral part of Australian crayfish culture. Although intensive growout of Cherax species
has been investigated (Kowarsky, 1984; Fernandez, 1988; Nardi, 1988), no commercial
success has been documented.
The application of intensive practises for specific market requirements is exemplified by the
development of soft-shell crayfish shedding systems in the United States. A gourmet market
exists there for post-moult crayfish (Procambarus clarkii), which are eaten whole while the
shell is soft. Whereas the random collection of soft-shelled individuals from production ponds
or natural systems would not be viable, the high price received for this product is sufficient to
justify intensive systems specifically designed to maximise moulting frequency (Culley et al.,
1985; Culley and Duobinis-Gray, 1987; Malone and Burden, 1988).
64
7.4.5
Flow-traps:
Although not widely documented, flow traps have been used with some success for a variety
of freshwater organisms. Their application to crayfish capture has previously been suggested
(Martin and Rodgers, 1982), although not generally accepted. By comparison, a considerable
research effort has been applied to baits and baited trap design (Bean and Huner, 1979; Brown
and Brewis, 1978; Westman et al., 1979a; Cange et al., 1986; Pfister and Romaire, 1983).
Cange et al. (1986) have indicated that as much as 50% of gross revenue may be expended on
harvesting in crayfish culture in the southern United States. The value of alternative methods
such as electro-fishing (Westman et al., 1979b) should be fully investigated. Clearly the utility
of flow trapping depends on specific water flow response. Fortunately, C. quadricarinatus has
a very strong flow response.
As a behavioural reaction of some complexity, C. quadricarinatus' response to current is likely
to be influenced by a host of parameters. Those of some measurable significance observed
included size of crayfish, source of water and flow rate.
Flow-trapped samples of C. quadricarinatus were generally biased towards larger individuals.
As juvenile crayfish, less than 1g have been observed to respond to water current as do adults,
this trapping bias is likely to be an artefact of hierarchical behaviour, whereby larger
individuals tend to displace smaller ones where both have a common goal. Such displacement
is most often observed in feeding.
The importance of water source in flow response is likely to be much closer to the root of this
innate behaviour. Traps supplied with water sourced from the same reservoir containing the
target population, consistently captured fewer crayfish than those with a 'foreign' water
supply. It would appear that the difference per se is of greater significance than the nature of
the difference. This equates with a natural dispersal mechanism which enables the species to
detect foreign water bodies which may be advantageously colonised. Upstream response
rather than downstream may be advantageous in regard to countering general downstream
movement caused by annual flooding. In addition, upstream localities are more likely to
support permanent water than those downstream where water may dissipate completely in the
impervious soils.
The significance of flow rate is likely to be a reflection of the C. quadricarinatus' capacity to
detect current and its mechanical ability (strength) to move against flowing water. Flow rates
less than 301/min may become decreasingly less detectable, while flow rates greater than
301/min may become increasingly difficult to move into. The trapping bias towards larger
individuals observed, may be related to the latter.
Based upon the results of all trapping exercises, it was clear that the submerged trap has
greatest application in a full pond for capturing samples of crayfish. A trap with a volume of
2001 consistently caught in excess of 200 crayfish from a pond population between 4,000 and
7,000. Partial harvesting using submerged flow traps may be possible, although there is likely
to be a threshold density below which the trap becomes ineffective.
Box and ramp traps are most effective as an adjunct to drain harvesting. They have been used
with great success at Walkamin at the final stages of drain harvest, but require the release of
some water from the inlet to stimulate the crayfish to move upstream. Incorporation of the
trap features into the pond floor may prove to be an even more effective harvesting method
(Fig.7.5).
65
7.4.6
Water Quality:
Acceptable water quality was maintained throughout the growout period. To achieve this,
constant (daily) attention was paid to water quality parameters. After some considerable
experience, many water quality parameters were gauged by visual inspection, however, actual
measurement of water temperature, pH and dissolved oxygen (DO) was made at least once
per week.
Water temperature is not a parameter over which any (cost effective) control can be exerted,
although solar technology may alter this in the future. It is important however, to consider the
desired temperature regime in regard to site selection and/or production strategy. It was clear
from the results of this study that water temperature was sub-optimal for at least 2 months
during winter. An alternative site may alleviate this, or as suggested previously, an earlier
stocking date may reduce the overall effect of reduced winter temperatures.
Dissolved oxygen is of fundamental importance in aquaculture and particularly so for crayfish
which are benthic and secretive. The importance of DO in crayfish culture has been clearly
stated (Avault et al., 1975; Melancon and Avault, 1977; Morrissy et al., 1984). Although
artificial aeration was not necessary in the growout ponds of this study, the use of mechanical
aerators, compressed air or other aeration devices is recommended for commercial operations.
Recent studies at the University of Queensland (Paterson et al., 1989) indicate that C.
guadricarinatus is particularly tolerant of low DO, and is able to continue respiring at DO
concentrations as low as 1ppm. Prolonged exposure to low DO however, results in an oxygen
debt for which several hours of recovery are required. C. guadricarinatus is somewhat more
tolerant of low DO than C. destructor and C. tenuimanus (Morrissy et al., 1984). Although
this is a positive attribute for when problems occur, sound water quality management should
ensure that DO remains optimal, in excess of 5ppm at all times.
Figure 7.5. Diagrammatic representation of crayfish pond in cross-section, incorporating
features of the 'box and ramp' flow trap. The trap or sump beneath the water inlet would be
covered during the growout period. At harvest, the pond is drained while a low flow-rate of
inlet water is maintained. As the pond nears empty, crayfish will move up the channel and
into the trap, in which a cage is installed. This can be removed by a mechanical arm (tractor
attachment) from the pond bank.
66
pH was maintained within the desirable range as suggested by Boyd (1979), of 6.5 to 9.0.
Under normal circumstances, a pH of this magnitude is not difficult to maintain, however,
some contingency should be made for the exception. Excessively low pH is rarely
problematic in Australian aquaculture, which contrasts dramatically with areas of the northern
hemisphere where acid rain has caused acidification problems (Malley, 1980; Patterson and
deFur, 1988). Liming of ponds at 1,000 to 2,000 kg/ha each year is generally sufficient to
maintain a desirable pH and good buffering capacity against dramatic changes (Boyd, 1979).
High pH can result from excessive productivity in the water and is best treated by flushing
(dilution).
Other water quality parameters are of importance to maximise production, but are generally
less dynamic in their fluctuations. Professional testing of water prior to the initiation of the
aquaculture venture will determine the need for specific treatment or at worst the unsuitability
of a particular site. Water hardness, and specifically Calcium levels are of particular
importance to crayfish aquaculture (Adegboye, 1983). Low levels result in poor growth, while
excessive levels may also be deleterious (Cripps and Nakamura, 1979). A range of 50 to 100
mg/1 CaC03 is recommended.
Appearance of undesirable algae generally results from particular water quality conditions.
Blue-green algae, such as Anabaena circinalis which developed in the ponds of this study, are
potentially dangerous if a massive die-off occurs and/or because of their toxic nature. The
conditions which lead to the colonisation of blue-green algae are related to nutrient levels in
the water (May and Baker, 1978; Boyd, 1979). To minimise the risk of blue-green algae
developing, ponds should be fertilized sufficiently to maintain a healthy phytoplankton bloom
at all times. If blue-green algae do develop, they are most effectively controlled by flushing
and heavy aeration, although other methods are also available (May and Baker, 1978).
The filamentous green algae which developed in pond 3 was also considered dangerous,
because of potential mass die-off and associated DO problems and most significantly, the
likely interference with harvesting. Filamentous green algae grow off the bottom, but can
form free-floating mats on the surface. Heinen et al. (1988) suggested skimming the pond
with a fine seine net, which may be effective but not curative. Aquatic herbicides, usually
containing copper, are not recommended because of the potential risk to the crayfish.
Maintenance of a healthy phytoplankton bloom or turbid water is the best prevention.
67
8
8.1
POST-HARVEST ASPECTS
Introduction:
All foods which originate from aquatic organisms, both marine and freshwater, are
collectively termed seafoods, and the processes applied to these organisms once they are
taken from their natural environment are collectively termed post-harvest processes. These
involve a chain of events including handling, processing and to some extent marketing, during
which the organism's sensory characteristics (appearance, flavour, texture etc.) must be
maintained at an optimal level.
Handling is considered the most important aspect of the whole processing chain. Procedures
employed at this stage are most influential to the subsequent quality of the product. A major
advantage of handling freshwater crayfish is that they are easily kept alive and are therefore
significantly less prone to degradation. Upon death, all aquatic organisms are susceptible to
the processes of deterioration and spoilage, which may include rigor mortis, autolysis,
melanosis, bacterial spoilage and oxidation. Live product in a healthy state is not subject to
these processes and has a greater potential of receiving optimal market response.
C. quadricarinatus is particularly well suited to live handling because it is both physically and
physiologically robust and extremely tolerant of exposure. Post-harvest aspects investigated
in this study were therefore restricted to determination of the sensory characteristics of C.
quadricarinatus and establishment of appropriate processing techniques.
These investigations required specialized food technology skills and facilities unavailable at
Walkamin Research Station. Assistance was therefore sought and received from the Food
Research and Technology Branch of the Department of Primary Industries. Sue Poole, a food
scientist based at the Food Research Laboratories at Hamilton, Brisbane, supervised the
conduct of this research and collated the results. The following information is based directly
on her report.
8.2
Materials and Methods:
All crayfish used for post-harvest studies were wild stock captured by trapping from rivers
and dams in the Mareeba District (Mitchell River Catchment). Crayfish were chilled and
packed into insulated boxes at Walkamin and then air-freighted to Brisbane. Upon arrival at
the laboratory (16-18 h transit) crayfish temperatures were 15-20°C. Only those crayfish
which arrived alive were used for sensory analyses.
Sample preparation: Crayfish were subjected to "cold-shock" treatment by placing them in a
freezer (-18°C) for 25-30 min prior to cooking. Crayfish were boiled in freshwater for 7 min
in a commercial prawn cooker and then immediately chilled in ice slurry for 5 min. This
standardized cooking method was used in all trials, unless otherwise stated.
Heads were removed and the tails rinsed briefly to remove gut contents. The tails were shelled
and deveined. Tail meats were cut into 2-4 portions (depending on animal size), which were
mixed and randomly distributed to each panellist. All crayfish were presented chilled.
Flesh Composition/Recovery: Proximate and cholesterol analyses were conducted to define
flesh composition characteristics. Proximate analysis involved the following methods:
moisture - oven drying method (100-102°C/16h), AOAC (1984) 24.003
fat
68
- modification of Bligh and Dyer method (1959).
protein - kjekdahl method, AOAC (1984) 24.027, 2.055, 2.057 (nitrogen x 6.25)
ash
- AOAC (1984) 18.025.
Cholesterol level in the tail flesh was determined at the Government Chemical Laboratory
according to the methods of Adams et al. (1986) and Kovacs et al. (1979).
Flesh recoveries were calculated for both raw and cooked crayfish. Flesh was defined as the
abdominal muscle, extracted by separating the tail from the head, splitting the tail shell and
removing the muscle in one piece. Estimation of claw meat recovery for large males was also
made.
Sensory Evaluation: Prior to commencement of sensory evaluation trials a questionnaire was
distributed among staff which asked for details concerning usual eating habits and frequency
of eating various crustaceans (both marine and freshwater). On the basis of the responses, a
sensory panel of 30 members was selected. Chosen members covered a wide range of tasting
familiarity with crayfish, from those who had never eaten it, to those who eat it often and
prepare it at home. Two types of sensory evaluation test were applied.
1. Acceptability testing
The sensory panel was presented with several samples, each labelled with a randomly
allocated 3-digit code. For acceptability, samples were scored on a 9-point hedonic scale, 9
corresponding to extremely acceptable and 1 corresponding to completely unacceptable
(Table 8.1). Additionally, panellists were asked to select descriptive words which best applied
to the flavour and texture of the flesh.
2. Difference testing
Difference testing was carried out by triangle tests in which each panellist received 3 samples:
2 were identical and 1 was different. The panellist was asked to decide which is the odd
sample and he/she MUST make a choice. The number of correct responses was totalled and a
significance table consulted which established whether there was a statistical difference
between the samples. Triangle tests were conducted according to Australian Standard
methods, AS 2542.2.2 (Standards Association of Australia, 1983) with the modification of the
following extra responses demanded:
•
•
•
rating of difference magnitude
sample preference
comments on reason for preference
Trials:
Freshwater/Brine Cooking
Batches of crayfish were boiled separately in one of 0, 1.5 or 3% saline solutions. Crayfish
were evaluated by acceptability testing in two replicate trials. A difference test between 0 and
3.0% saline was also conducted.
Cooking Methods
69
Three cooking methods were compared: boiling, steaming and microwaving. Similar size
crayfish (wet weight) were used for individual trials to ensure cooking conditions were
equivalent for all animals. Crayfish were boiled as per the standard method. Steamed crayfish
were held for 7 min in a covered wire basket, over rapidly boiling water. Microwaved
crayfish were cooked as whole animals for 20 min on a medium low setting (320 watts). The
difference test was applied.
Male/Female Comparison
Male and female crayfish of equivalent size were cooked as per the standard method, and
compared using difference testing.
Size of Animal
Crayfish were divided into 2 size groups as follows, cooked as per the standard method and
evaluated with the difference test.
• large: >140g 9 animals, range: 140-239g, mean weight 164g
• small: <100g 12 animals, range: 76-99g, mean weight 91g
Tail/Claw Meat Comparison
Claw meat from 33 animals was required to produce a sufficient sample size. The difference
test was used.
Comparison of Cherax species
Acceptability trials were conducted to determine how C. quadricarinatus compared with
marron (C. tenuimanus) and yabbies (C. destructor). Marron were obtained from a farm in
North Queensland and yabbies from a farm in Victoria. All crayfish were delivered live to
Brisbane. Cooking was by the standard method except that yabbies were boiled for 6 min and
marron for 10 min. Trials were replicated three times.
Comparison of Popular Seafoods
Three replicate acceptability panels were carried out with aquacultured tiger prawns (Penaeus
esculentus), Tasmanian rock lobster (Jasus species), Moreton Bay Bug (Thenus orientalis)
and C. quadricarinatus. All species were obtained live (except the bugs which were fresh
chilled, green) and cooked in 3% brine for varying times: prawns, 3 min; lobster, 15 min;
bugs, 12 min and C. quadricarinatus, 7 min.
Saline Conditioning Comparisons
A one off acceptability trial was carried out with C. quadricarlnatus that had been maintained
alive in 0, 0.6, 1.2, 1.8 and 2.4 % saline for 3 weeks (Chapt.3). Following this, difference
testing was carried out with crayfish "conditioned" in brines (of varying salinity) for different
time periods and crayfish which remained in freshwater until harvest.
Frozen Storage of Trials
70
Live crayfish were subjected to "cold shock" treatment and packed, 10 animals per pack, in
oxygen impermeable Cryovac barrier bags. The bags were heat sealed and frozen at -18°C in
a domestic chest freezer for up to 6 months.
Four treatments were compared:
1.
2.
3.
4.
Frozen cooked - whole crayfish cooked and chilled by the standard method.
Frozen green tails - heads were removed and tails only frozen.
Frozen green - whole green crayfish were frozen.
Frozen green blocked - whole green crayfish packed with enough fresh water to
encapsulate the animals.
At monthly intervals, one pack of each of the four treatments was thawed in running cold
water (approximately 1 hour). The frozen green animals were cooked and chilled by the
standard method. Tail flesh from all four treatments was presented to each of twenty
panellists for acceptability evaluation. Additionally at each sample time, the total number of
bacteria present on the tail flesh was determined as well as K-value. K-value analysis
determines the nucleotides present in the flesh and is commonly used as a freshness indicator.
Hedonic Scale
Description
9
8
7
6
5
4
3
2
1
like extremely
like very much
like moderately
like slightly
neither like nor dislike
dislike slightly
dislike moderately
dislike very much
dislike extremely
Table 8.1. Hedonic scale description for sensory evaluation of Cherax quadricarinatus.
8.3
8.3.1
Results and Discussion:
General Observations
A preliminary trial was carried out to establish the parameters for the standardized cooking
method. Crayfish of similar size (80-1OOg) were boiled for 5, 6, 7, 8, 9 and 10 mins and
assessed by 3 staff for cookedness. It was considered that 7 min boiling resulted in the best
eating quality animal which was cooked through but retained characteristic flavour and
tender, slightly resilient flesh. Hence, 7 min was used for all subsequent cooking of C.
quadricarinatus.
It was found to be important to use only live crayfish for experimental work. Those crayfish
that died in transit often exhibited a strong ammoniacal odour which remained after cooking
and was reflected in their flavour. Additionally, it was found that dead animals had very poor
quality texture, when cooked. The textural changes ranged from weak fibre texture and
slightly mushy to flesh with a similar consistency to paste. The degree of flesh degradation
71
(and the intensity of ammoniacal odour/flavour) is likely to be dependent upon the length of
time the animal was dead and be a result of proteolytic enzyme activity. Such activity is
known to proceed very rapidly in crustacean species (Rowland et al., 1982). The significance
of these observations is, that if C. quadricarinatus are to be marketed live, care must be taken
to ensure that dead animals are discarded to avoid negative reaction within the market.
8.3.2
Flesh Composition - Proximate Analysis
A summary of results, grouped by different biological attributes, is presented in Table 8.2.
The composition of flesh from C. quadricarinatus seems relatively consistent and similar to
both freshwater and marine crayfish species (Dabrowski et al., 1966; Sidwell et al., 1974;
Vlieg, 1988). There appeared to be no differences between male and female animals nor
between large and small animals. In addition, crayfish from different sources had similar
proximate composition. With crayfish subjected to a period in salt water prior to harvest, the
moisture content was less than those which remained in freshwater throughout (Table 8.3)
and, from the limited results obtained thus far, it appears that moisture loss is related to time
exposed to salt water. Moisture loss equates to live weight loss and for crayfish "conditioned"
in 2.5% saline for 24h, the weight loss is about 3%. However, for animals in 2.5% saline for
48h the weight loss increased to around 7%. Under salt conditions such loss of moisture is
expected but needs to be kept in mind from an economic point of view.
Flesh source
N
Moisture
Fat
Ash
Total N
Protein
(nett)
pH
Overall (raw)
18 80.75 (0.33) 0.72 (0.01) 1.33 (0.02) 18.38 (0.20) 14.15 (0.27) 6.50 (0.03)
Males (54-135g)
9 80.23 (0.37) 0.73 (0.03) 1.36 (0.03) 18.63 (0.32) 14.24 (0.47) 6.44 (0.06)
Females (43-126g) 9 81.27 (0.35) 0.72 (0.02) 1.30 (0.01) 18.12 (0.17) 14.06 (0.35) 6.55 (0.33)
Small (50-71g)
7 80.10 (0.50) 0.70 (0.00) 1.31 (0.03) 18.51 (0.41) 14.17 (0.21) 6.48 (0.03)
Large (126-135g)
3 80.80 (0.60) 0.70 (0.00) 1.31 (0.01) 17.91 (0.07) 13.43 (0.07) 6.53 (0.01)
Dead animals
9 78.00 (0.80) 0.90 (0.00) 1.95 (0.11) 17.91 (1.47) 13.34 (1.65) 6.92 (0.12)
Cooked flesh
20 81.10 (0.30) 0.55 (0.05) 1.09 (0.06) 17.26 (0.42) 14.03 (0.60) 7.10 (0.06)
Clawmeat : raw
30
86.00
0.50
1.25
12.93
9.99
6.40
cooked
15
80.70
0.50
1.17
17.16
14.58
7.70
Table 8.2. Proximate analysis of flesh of Cherax quadricarinatus expressed as percentages.
Bracketed numbers are the standard error of the mean. ** expressed as protein using a
conversion factor of 6.25.
72
Flesh source
N Moisture Fat Ash Total N* Protein pH NaCl
nett
0% saline
5
79.5
0.8 1.44
18.08
14.11
6.5
0.22
2.5% saline (24 hrs)
4
77.2
0.7 1.57
20.95
16.64
6.5
0.41
0% saline
5
82.1
0.6 1.89
17.27
13.75
6.5
0.38
2.5% saline (48hrs)
5
76.5
1.0 1.68
21.26
16.70
6.5
0.57
Table 8.3. Proximate analysis of Cherax quadricarinatus exposed to saline conditions,
expressed as percentages. * expressed as protein using a conversion factor of 6.25.
8.3.3
Flesh Composition – Cholesterol
Cholesterol present in C. quadricarinatus ranged from 180 mg to 250 mg/100g flesh, with a
mean of 222 mg/100g flesh. This is higher than cholesterol levels reported for many marine
lobsters, which ranges from 85-208 mg/100g flesh (Pihl, 1952; Kritchevsky et al, 1967;
Feeley et al. 1972 and Cashel, 1985). It is also higher than cholesterol levels reported for
other Australian crayfish species: (mg/100g wt) Sydney rock lobster, 79; tropical lobster, 58;
West Australian lobster, 52 (Pearson, 1977). Levels of cholesterol in C. quadricarinatus are
similar to those present in many species of marine prawns.
8.3.4
Flesh Recovery
Raw flesh recovery ranged from 14.5 to 36.9% of whole body weight, with a mean of 22.2%.
The broad range is likely to be a reflection of different physiological states related to the
moult cycle.
The cooked flesh recovery from C. quadricarinatus, boiled 7 min and ice-slurry chilled 5 min,
averaged around 23% of wet weight (Table 8.4). This recovery is similar to, although a little
lower than that achieved for marron, but significantly higher than for yabbies. Compared with
flesh recoveries from marine species, that of C. quadricarinatus is similar to crabs but lower
than Moreton Bay bugs, rock lobsters and prawns. Flesh recovery from claws was low and
was related to claw size. For animals with a wet weight of 100 to 180g and claw weight of 20
to 50g, claw meat recovery was about 5g which corresponds to a recovery rate of around
4.5%.
Whole wet weight of C. quadricarinatus included in the analysis ranged from 29.3 to 238.6g
and although the percentage recovery range was similarly wide, there was no obvious trend
between animal size and flesh recovery. In fact, the 2 variables appeared to be independent, as
illustrated by percentage flesh recovery from animals with the same wet weight differing by
as much as 10%. However, when animals were divided into 2 size groups (>100g and <100g)
and the average percentage flesh recovery for each group was calculated, the smaller crayfish
demonstrated a higher percentage flesh recovery (Table 8.4). This finding could well be
related to biological development of C. quadricarinatus. Significant claw growth is not
apparent until the animal reaches 80 to 100g in size.
73
Species
Percentage Recovery
N
Range
Mean
Standard Error
Total
130
9.8-53.2
22.8
0.004
> 100g
40
9.8-27.5
20.5
0.006
< 100g
81
14.3-53.2
24.1
0.005
C. tenuimanus (marron) 37
21.7-30.0
26.2
0.003
37
7.7-17.4
12.0
0.003
C. quadricarinatus
C. destructor
Prawns
Crabs
Rock Lobster
Moreton Bay Bugs
49- 52
25- 30
40- 45
28- 30
Table 8.4. Cooked flesh recoveries for three species of Cherax. 1 values for other seafood
species were not determined in this investigation, but are generally accepted.
8.3.5
Freshwater/Brine Cooking
Results from the replicate trials were averaged and are presented in Figure 8.1. The mean
hedonic scores for crayfish cooked in 0, 1.5 and 3% saline were 6.98, 7.15 and 7.35
respectively. The differences between these scores was not statistically significant although
the animals cooked in the brine solutions were more frequently described as "sweeter/better
flavour". There was no difference in flesh recoveries from crayfish cooked in any of the salt
solutions.
A difference test carried out between 0 and 3% saline cooked crayfish indicated that only a
limited number of panellists could detect a difference (10/29) and hence, the difference was
not
74
Figure 8.1. Mean hedonic preference scores for Cherax quadricarinatus boiled in freshwater,
1.5% saline and 3.0% saline. Hedonic scores are described in Table 8.1.
statistically significant. Of the correct responses, all indicated that the difference was slight
and 7 preferred the 0% cooked crayfish and 3 preferred the crayfish cooked in 3% brine.
Summary: Cooking crayfish with or without salt had no significant effect on their flavour.
8.3.6
Cooking Methods
Results of the separate difference tests are summarized in Table 8.5. For boiled/microwaved
and steamed/microwaved comparisons less than half the panellists detected a difference and
hence, statistically, there is no significant difference between the methods of cooking.
However, it was interesting to find that panellists who correctly identified a difference made
similar comments. The microwaved and steamed crayfish were described as "less
watery/more flavour/better taste/better flesh colour (oranger)" compared to the boiled crayfish
described as "firmer textured/lacked flavour/watery".
Comparison
Number of
correct responses
Boiled/
steamed
Boiled/
microwaved
Steamed/
microwaved
6/30
11/30
11/30
75
Significance
NSD
NSD
NSD
Degree of difference:
slight
moderate
much
extreme
4
1
1
0
6
4
1
0
8
2
1
0
Preference: Boiled
Steamed
3
3
Boiled 3
Microwaved 8
Steamed 7
Microwaved 4
Table 8.5. Difference test results and flavour preference of Cherax quadricarinatus cooked by
three methods. NSD - not significantly different (p<0.01).
The apparent complete similarity in flavour of boiled and steamed crayfish was somewhat
unexpected. Similar tests conducted with mudcrabs (results not reported here) indicated a
large difference between boiled and steamed animals, with those cooked by steam preferred
over the boiled animals.
Flesh recoveries attained with the different cooking methods are summarized in Table 8.6.
There was significantly higher percentage flesh recovery from boiled crayfish than from other
animals. This is likely to be due to water retention and/or absorption when the animal is
immersed in water (boiling). This is further exemplified by microwaved crayfish which
showed the lowest percentage flesh recovery, as microwaving could be expected to drive off
moisture. Weight losses caused by cooking method, relative to boiled flesh weight, were 11%
for steamed and 27% for microwaved animals. Such large weight losses are important when
choosing a cooking method within a commercial operation.
Summary: Method of cooking has limited effect on the flavour of C. quadricarinatus and as
boiling resulted in the best percentage flesh recoveries, it was used as the cooking method for
subsequent trials.
Percentage Recovery
Cooking Method
N
Range
Mean
Standard error
Boiled
30
22.7- 31.7
26.6
0.004
Steamed
30
15.8-32.5
23.6
0.008
Microwaved
31
8.3-44.0
19.5
0.015
Table 8.6. Percentage flesh recovery from Cherax quadricarinatus cooked by three methods.
Means are significantly different (p<0.05).
76
8.3.7
Male/Female Comparison
Sensory analysis indicated that there was no significant difference in flavour between male
and female crayfish (Table 8.7). When the difference was correctly detected (13 out of 30
panellists) it was mostly considered to be slight. For those panellists who were able to pick
differences, most preferred the flavour of male animals and comments received included
"slightly tastier/better flavour/slightly more flavour".
Summary: Sex of animal is unimportant with respect to flavour, but if a choice was relevant,
it is recommended to retain females and market the males.
8.3.8
Size of Crayfish
Results of sensory analysis showed that there was a significant difference (p<0.05) in flavour
between large and small crayfish (Table 8.7) although the difference was most often
considered slight. The preference was for small (<100g) crayfish as they were considered to
have more flavour.
Summary: Based on flavour of the crayfish, it is preferable to harvest at <100g. Such a
recommendation does not allow for other market factors, eg. visual presentation in
restaurants.
8.3.9
Tail/Claw Meat Comparison
All panellists were able to detect a difference between the two types of meat (Table 8.7). The
difference was considered moderate to much and differences in appearance, texture and
flavour were commented on. There was a strong preference (93% of panellists) for claw meat
compared to tailmeat with claw meat described as "more flavour/sweeter". These results are
similar to those obtained with other clawed crustaceans such as marine lobsters and mudcrabs.
Comparison
male/female
size class
clawmeat/tailmeat
Number of
correct responses
13/30
16/30
30/30
Significance
NSD
p<0.05
p<0.01
9
4
0
0
9
4
2
1
4
9
13
3
Degree of difference:
slight
moderate
much
extreme
Preference:
male 11
female 12
< 100g
13
> 140g 3
claw 28
tail 2
77
Table 8.7. Difference test results and flavour preference for different biological attributes of
Cherax quadricarinatus. NSD -not significantly different (p<0.05).
Summary: There was a definite difference in flavour between claw and tail meat, with claw
meat considered preferable due to its better flavour.
8.3.10 Comparison of Cherax species
Sensory analysis showed that C. quadricarinatus rated similarly to marron (mean scores of 6.9
and 7.1 respectively) and better than yabbies which had a mean score of 4.7. The descriptive
words chosen to describe the flavours present in C. quadricarinatus and marron were very
similar (Figure 8.2) although C. quadricarinatus were more frequently described as bland
compared to marron. Yabbies had an over-riding cabbage-like flavour which resulted in their
low score. The texture of all species was similar and most frequently described as
"moderately tender/optimum texture".
A similar trial comparing sensory characteristics of both pond and battery reared marron and
yabbies (Gazey et al., 1987), found little difference between groups. It is apparent that the
flavour and other characteristics of the 3 Cherax species are similar, but can be significantly
altered by unknown factors.
Summary: C. quadricarinatus had a little less flavour than marron, but compared favourably.
A repeat trial should be carried out between C. quadricarinatus and yabbie using animals
which do not have the cabbagey flavour before a valid comparison can be made.
78
Figure 8.2. Sensory evaluation comparison of Cherax quadricarinatus , C. tenuimanus
(marron) and C. destructor (yabbie) flesh. Preference scores refer to the hedonic scale
described in Table 8.1.
8.3.11 Comparison of Popular Seafoods
Preference ratings and flavour profiles are presented in Figure 8.3. Prawns rated extremely
well (mean score 7.7) and were described as having a sweet, fresh flavour. Lobsters, Moreton
Bay Bugs and C. quadricarinatus rated similarly (mean scores: 7.0, 6.6 and 6.8 respectively.
Interestingly, C. quadricarinatus were not described as bland more frequently than lobsters
used in the analysis. The relatively low score given to Moreton Bay bugs may have resulted
from the presence of "bitter/salty" flavours present. It is suspected these animals may have
been dipped in metabisulphite which can result in bitter/salty flavour in cooked product. The
texture for all species was similar and described as "optimum texture".
Summary: C. quadricarinatus rated very well in direct comparison with marine seafoods. The
result was a little surprising as the marine seafoods are more commonly eaten and therefore
known to the panellists, which can affect preference rating in this sort of analysis.
Figure 8.3. Sensory evaluation comparison of Cherax quadricarinatus, Penaeus esculentus
(tiger prawn), Jasus species (rock lobster) and Thenus orientalis (Moreton Bay bug) flesh.
Preference scores refer to the hedonic scale described in Table 8.1 .
8.3.12 Saline Conditioning Comparisons
79
Results of acceptability and flavour descriptions are presented in Figure 8.4. The mean
acceptability scores were 5.8, 6.2, 6.1, 6.8 and 6.3 for crayfish grown inO, 0.6, 1.2, 1,8 and
2.4 percent saline respectively. With the qualification that the results are from one trial only, it
appears that animals held in salt water are preferred to those harvested directly from
freshwater. Many flavours were detected in crayfish taken from freshwater (Fig. 8.4) whereas
flavour types were more limited (or less detectable) for those crayfish held in saline.
Additionally, the higher salt concentrations resulted in crayfish which were more frequently
described as sweeter.
From the outcome of this one trial, it was considered there may be some possibility of being
able to adapt the flavour of C. quadricarinatus by "conditioning" the animals in salt water for
Figure 8.4. Sensory evaluation comparison of Cherax quadricarinatus flesh taken from
crayfish exposed to varying salinities for 21 days. Preference scores refer to the hedonic scale
described in Table 8.1.
a period prior to harvesting. Subsequent conditioning involved different salinities for varying
periods, assessed by difference testing.
Results are summarized in Table 8.8. Crayfish held in 2.5% for either 48 or 55 hours were not
significantly different in flavour from crayfish held in freshwater. For those responses which
were correct, the difference was considered slight to moderate. However, there was a definite
preference indicated for the crayfish conditioned in salt water and the universal reason was
that the flavour was better. Flavour descriptions most frequently chosen included "better
flavour/ sweeter/saltier" and a "lack of cabbagey flavour/no after taste" was noted.
80
The flavour of crayfish which had been held in 3.0% for 48 h was significantly better than
non-conditioned crayfish and for this sensory evaluation the difference was considered
moderate to much. Again, a strong preference for the saline crayfish was indicated.
Comparison
fresh /
2.5% 24hr
fresh /
2.5% 55hr
fresh /
3.0% 48hr
Number of
correct responses
11/30
9/30
18/30
Significance
NSD
NSD
p<0.01
5
5
1
0
4
4
1
0
2
9
6
1
Degree of difference:
slight
moderate
much
extreme
Preference:
NaCl content (%)
fresh 0
conditioned 11
fresh 0.22
conditioned 0.41
fresh 2
fresh 1
conditioned 7
conditioned 17
fresh 0.38
fresh 0.40
conditioned 0.57 conditioned 1.02
Table 8.8. Difference test results and flavour preference for saline conditioned Cherax
quadricarinatus. NSD - not significantly different (p<0.05).
Further definitive trials are required to fully explore the potential for flavour enhancement of
C. quadricarinatus through saline conditioning. This process has been applied to penaeid
prawns (Papadopoulos and Finne, 1986) and produced significant flavour differences. These
difference have been attributed to the changes in relative concentrations of amino-acids which
are involved in the osmo-regulatory process (McCoid et al., 1984; Papadopoulos and Finne,
1986). It is well established that the desirable crustacean flavour of prawns, lobsters and
crayfish is produced by particular amino-acids and their relative concentrations in the muscle
tissue (Konosu et al., 1960; Hashimoto, 1965; Hayashi et al., 1981). Under saline stress, the
concentrations of these amino-acids is altered, with a consequent flavour change. It may be
possible to define a particular salinity and treatment duration which results in optimal flavour
characteristics for C. quadricarinatus.
8.3.13 Frozen Storage Trials
Results of sensory evaluations are given in Figures 8.5 to 8.9 and show there was very little
deterioration over 6 months storage for any of the attributes measured. Additionally, there
81
Figure 8.5. Mean hedonic preference scores (9-1) for odour of Cherax quadricarinatus after
frozen storage up to six months. Storage treatments are described in the text. Hedonic scores
are described in Table 8.1.
82
Figure 8.6. Mean hedonic preference scores (9-1) for appearance of Cherax quadricarinatus
after frozen storage up to six months. Storage treatments are described in the text. Hedonic
scores are described in Table 8.1.
Figure 8.7. Mean hedonic preference scores (9-1) for flavour of Cherax quadricarinatus after
frozen storage up to six months. Storage treatments are described in the text. Hedonic scores
are described in Table 8.1.
83
Figure 8.8. Mean hedonic preference scores (9-1) for texture of Cherax quadricarinatus after
frozen storage up to six months. Storage treatments are described in the text. Hedonic scores
are described in Table 8.1.
Figure 8.9. Mean hedonic preference scores (9-1) for overall acceptability of Cherax
quadricarinatus after frozen storage up to six months. Storage treatments are described in the
text. Hedonic scores are described in Table 8.1.
was little difference between freezing treatments although the frozen cooked crayfish had the
least acceptable flavour (Figure 8.7).
Bacterial numbers present in all animals frozen green were low and ranged from 10-15 cfu/g.
As expected, the cooked frozen animals had a lower count of 1.0 x 10 cfu/g. These counts did
not change during the storage period.
K-values after 1 week of storage ranged from 1.6% to 9.8% and remained <10% throughout
storage. While no reports have been sighted in the literature of K-values of crayfish flesh, the
accepted level indicating excellent quality fish flesh is 20%.
Summary: Results of this trial indicate that C. quadricarinatus can be frozen with little loss of
quality. However, it is recommended that if freezing is to be carried out, animals should be
green rather than cooked, due to flavour loss with time in the frozen cooked product.
8.4
Conclusion:
These results provide a sound understanding of the sensory attributes characteristic of C.
quadricarinatus, and basic processing procedures which will ensure optimal product quality. It
is clear that C. quadricarinatus has excellent sensory attributes which will place it in the
gourmet seafood range along with rock lobster, bugs and high quality prawns. Opinion from
84
some quarters has suggested that the flavour of C. quadricarinatus (and indeed all freshwater
crayfish) is excessively mild. This is clearly not problematic to those established markets,
such as Europe, which are accustomed to freshwater crayfish characteristics. Saline
conditioning may provide the mechanism for flavour enhancement to satisfy more specific
market requirements for stronger flavoured seafood. In addition, future food research should
focus on further (secondary) processing which maximises the acceptability of C.
quadricarinatus. This should involve development of recipes, methods of presentation and
value adding processes.
85
9
9.1
GENERAL BIOLOGY Cherax quadricarinatus
Introduction:
Freshwater crayfish are familiar to many Australians whether through fishing exploits as a
youngster, culinary experience at a restaurant or through more contemporary exposure to
crayfish aquaculture. Despite this familiarity, the biology of these creatures, which may or
may not be of interest, is generally poorly understood. From an aquaculture perspective this is
undesirable, as a basic but sound understanding of the animals anatomy, physiology and
behaviour is an essential prerequisite to successful crayfish farming.
Cherax quadricarinatus is a typical freshwater crayfish and therefore, the substantial body of
biological information documented for other species is generally applicable. Recent
publications by Holdich and Lowery (1988) and Mills (1989) contain thorough descriptions of
crayfish biology. Information presented here represents only the most basic aspects of biology
specific to C. quadricarinatus. It is recommended that other references, such as those
suggested, are perused to obtain a complete understanding appropriate to a successful
aquaculture venture.
9.2
Systematics and Distribution:
Freshwater crayfish are crustaceans, a group including the crabs, prawns and lobsters.
Crustaceans and insects are close relatives and are grouped together with spiders, millipedes
and centipedes as Arthropods (Fig. 9.1). This association is of more than academic interest, in
consideration of pesticides.
The majority of pests affecting agriculture are insects for which an enormously wide variety
of poisons (insecticides) have been developed. Because of their close relationship, crustaceans
are in most instances as equally susceptible to insecticides as the insects themselves. Most
aquaculture developments occur on or near to land previously or presently used for
agriculture and likely to have had insecticide application. The utmost care should be taken to
ensure insecticide and other pesticide use is eliminated or at least minimised in the vicinity of
crayfish aquaculture.
All freshwater crayfish belong to one of three families (Fig.9.1). Two of these, Astacidae and
Cambaridae occur only in the northern hemisphere. The remaining family, Parastacidae is
restricted to the southern hemisphere and contains 13 genera including Cherax. Australian
crayfish with aquaculture potential all belong to the genus Cherax.
C. quadricarinatus is a tropical species occurring in the river systems of Queensland and the
Northern Territory draining to the Gulf of Carpentaria, some eastward flowing rivers of
northern Cape York, coastal rivers west of the Gulf and in south-eastern New Guinea.
86
Arthropods
Others
Insects
Crustaceans
Malacostraca
Several groups
Crabs, Shrimps
Prawns, Lobsters
Crayfish
Mostly very small
Freshwater Crayfish
Astacida
Astacidae
Northern hemisphere
Cambaridae
Northern hemisphere
Parastacidae
Southern hemisphere
13 genera
including Cherax
Cherax destructor
Yabby
Cherax tenuimanus
Marron
Cherax quadricarinatus
Redclaw
Figure 9.1. Systematic information for freshwater crayfish. Position within the
arthropods (top), and the freshwater crayfish families (bottom).
9.3
Anatomy:
Figure 9.2 illustrates basic anatomical characteristics of Cherax quadricarinatus. The body is
broadly divided into the abdomen (tail) and the cephalothorax (head) which is covered by the
carapace (shell). The carapace protects the internal body organs and is armoured at the front
with a strong pointed rostrum. Although the eyes are quite prominent eyesight is relatively
poor and the major sensory organs are the large feelers called antennae and the finer more
central feelers, the antennules. Antennae are used mostly as touch sensors while the more
sensitive antennules are used for both touch and taste, particularly in location of potential
food and sensing water parameters such as temperature and salinity. Because of their sensory
significance, it is important that crayfish are not handled by these organs.
The large claws (chelipeds) and the four pairs of walking legs behind them are called
pereiopods, numbered from front to back as 1 to 5. Both chelipeds and pereiopods 2 and 3 are
equipped with claws (chelae). Pereiopods 4 and 5 have simple pointed ends.
The abdomen is made up of six segments each encased in hard shell but able to articulate with
those adjacent because of a flexible membrane. Abdominal segments 2 to 5 each have a pair
of appendages on the underside (ventral side) termed pleopods (swimming legs). Female
crayfish attach their eggs to fine hairs (setae) on the margins of the pleopods. On the sixth
abdominal segment the pleopods have become enlarged and are called uropods. Together with
the central and terminal flap known as the telson these appendages constitute the tail fan used
to create thrust when the crayfish needs to move quickly. Females also use the tail fan to
create a temporary brood chamber to protect the eggs during incubation.
Physical differences between male and female C. quadricarinatus are reasonably clear (Fig.
9.3). The male cheliped (large claw) is relatively large and swollen compared to that of the
female and in addition has a soft, bright red membrane on its outer surface. The function of
87
Dorsal View
Carapace
Abdomen
(Tail)
Eye
Rostrum
Uropods
Antennules
Telson
Cheliped
(Claw)
Antennae
Walking legs
(pereiopods 2-5)
Ventral View
Pleopods
Anus
Mouth
Figure 9.2. Generalised illustration of dorsal and ventral aspect of Cherax quadricarinatus,
depicting anatomical features.
88
Female
Female
gonopores
Anterior
Chelipeds
Walking legs
Posterior
Male
Male
gonopores
Figure 9.3. Ventral aspect of female (top) and male (bottom) Cherax quadricarinatus showing
position of gonopores.
this red patch is not clearly understood but is thought to be involved in mating behaviour. On
the underside of the female gonopores from where eggs are released are situated at the base of
the third pereiopods while the male gonopores are at the base of the fifth pereiopods (Fig.9.3).
Juvenile crayfish less than 20 to 30g can only be sexually distinguished by the gonopore
position.
89
Two other anatomical features are of particular significance; the statocyst and gastrolith.
Statocysts are the crayfish balancing organs and each consists of a small chamber within the
shell located beneath the base of the antennules. Within each chamber there is a lump of soil
particles glued together called a statolith. The walls of the statocyst chamber are covered in
sensory hairs which are stimulated by the statolith as it rolls around. In this manner the brain
receives messages which it interprets to maintain correct orientation and posture. During
moulting the statolith is lost and must be replaced so it is important that some fine sand or soil
be present wherever crayfish are held for growout.
Gastroliths are small white stones deposited in the front of the stomach (Fig. 9.4). There are
two of them, and they are shaped like a thick saucer. Although present in the stomach at all
times, they become greatly enlarged just prior to moulting. There function is to store calcium
used in the hardening of the new shell after moulting. Gastroliths present on the floor of a
tank indicate that newly moulted (soft) crayfish have been cannibalised by others.
Figure 9.4. Diagrammatic representation of a freshwater crayfish, showing location of
gastrolith deposition in the stomach (a) and gastrolith profile from back (b), front (c) and side
view (d). Modified from Olszewski (1980).
9.4
Morphometric Relationships:
Morphometric relationships are those that describe mathematically the correlation between
body measurements. The standard against which other parts are related is, for crayfish, the
carapace length (orbital carapace length), or sometimes weight. Carapace length is measured
from behind the eye to the posterior edge of the carapace. Other measurements sometimes
recorded, but less reliable, are the rostral carapace length measured from the tip of the rostrum
to the posterior edge of the carapace, or the total length, measured from the tip of the rostrum
to the posterior edge of the telson.
90
For C. quadricarinatus the nature of some often used morphometric relationships is described
by the following functions, where:
Carapace length (mm) =
Weight (g) =
Rostral carapace length (mm) =
Total length (mm) =
Meat weight (g) (i.e. the edible portion) =
Sample size =
Correlation coefficient r² =
WT =
WT =
RCL =
TL =
MW =
0.00054 x (CL) 3.04
0.0000282 c (TL) 2.95
1.483 x CL – 0.081
3.139 x CL – 0.671
0.214 X WT + 0.608
CL
WT
RCL
TL
MW
N
r²
N = 599
N = 599
N = 164
N = 164
N = 55
r² = 0.999
r² = 0.998
r² = 0.998
r² = 0.996
r² = 0.911
These functions can be used with a high degree of confidence to estimate a given parameter
when the measurement of only one other is known. For example, knowing the total length to
be 100.0mm, an estimate of weight can be calculated as 0.0000282 x (100.0)2.95 which equals
22.4g.
9.5
Life Cycle:
A major aquaculture advantage of crayfish in comparison to other crustaceans and fish is the
simplified life cycle. The most outstanding characteristic is the absence of free living larval
stages.
A diagrammatic illustration of the C. quadricarinatus life cycle is given in Fig. 9.5.
Successful reproduction results in a brood of fertilized eggs which are carried and carefully
nurtured by the mother. Fecundity varies with female size (Chapt.6), ranging from <300 to
>1000. Incubation takes from 6 to 10 weeks during which time the tiny crayfish pass through
their larval stages within the confines of an egg case, actively protected by the parent.
Hatching sees the release of miniature crayfish (0.02g), of adult form, which continue to use
their mother as a refuge for some days before becoming completely independent.
Under appropriate conditions of habitat and food availability, hatchling crayfish grow
quickly achieving a size of 0.5 to 1.0g in 50 to 60 days. These juvenile crayfish continue to
grow rapidly and will reach 50 to 100g and sexual maturity within 12 months. Reproduction
may occur more than once through the summer months, during which moulting frequency and
growth is maximal. A maximum size of 300g has been recorded for Mitchell River stock,
although some genetically independent stocks have been reported to achieve 600g. The
maximum size probably relates to an age of 4 to 5 years.
91
Mating
during summer
Adults will grow to
300g+
4-5 years max.
Mature
50-100g,
market size
Incubation
6-10 weeks
REDCLAW
Hatchlings
adult form, 0.02g,
300-1,000/ female
Rapid growth,
50-60 days fed
zooplankton
Rapid growth,
6-12 months
fed detritus
Juvenile
0.5 - 1.0g
benthic
Figure 9.5. Diagrammatic illustration of the Cherax quadricarinatus life cycle.
9.6
Reproduction:
Reproduction for C. quadricarinatus is primarily related to water temperature, although day
length may also have some influence (Chapt.6). In those parts of the distribution where winter
water temperature falls below 20°C, there is a recognisable spawning season which is initiated
through July/August as water temperature and day length increase rapidly (Fig.9.6). Spawning
takes place throughout the spring and summer months and individual females may carry two
or more broods of eggs. Preparation for mating for the female involves a period of ovary
conditioning and pleopod cleaning, however, a pre-copulatory moult as described for other
crustaceans (Phillips et al., 1980) is not necessary.
Mating has not been witnessed at Walkamin, however, the report of Sammy (1988) suggests
that the behaviours involved are similar to those described for several other crayfish species
(Mason, 1970; Pippin, 1977; Woodlock and Reynolds, 1988a). The male manipulates the
female into a position on top, with the ventral sides together (Fig.9.7). A sticky white mass of
sperm (the spermatophore) is then deposited by the male on the female shell, between the
walking legs. Over the next 12 to 24 hrs the female releases her eggs which are directed into a
temporary brood chamber formed by the tightly curled tail. This is achieved by way of a
water current created by the beating of the pleopods. The sperm packet is then broken open
with the sharp tips of the 5th pereiopods, releasing sperm which are also drawn into the brood
chamber. Fertilization takes place in the brood chamber after which the eggs become firmly
attached to fine
92
Figure 9.6. Annual water temperature and photoperiod profile at Walkamin (Lat 17.0°S Long
145.5°E Alt 900m), showing periods of reproductive stimulus and spawning for Cherax
quadricarinatus
Figure 9.7. Notional mating position of Cherax quadricarinatus, based upon observations of
Sammy (1988) and other literature (see text). From Olszewski (1980).
hairs on the margins of the pleopods. At this stage the eggs are oval, approximately 2mm in
length and olive green in colour. Over the next 4 to 6 weeks nurturing of the eggs by the
mother involves frequent probing and cleaning with the 5th pereiopods and regular fanning of
the pleopods to ensure oxygen supply. As the eggs develop, a sequence of colour and other
morphological changes occurs (Chapt.6), culminating in hatching at about 6-8 weeks. For a
period of 1 to 2 weeks the hatched crayfish remain attached to the pleopods, but soon after,
93
they break free. The independent crayfish begin to make forays of gradually increasing
distance and duration, returning to the mother for refuge. Within a week, they have become
entirely independent.
9.7
Growth:
Growth for crayfish involves the periodic shedding of the shell in a process called moulting.
Each moult results in new shell somewhat bigger than the last, so that growth is effectively a
series of steps.
Moulting is physiologically traumatic for the crayfish, and although moulting processes are
occurring at all times, it is during the few days prior to and after the shedding of the shell
(ecdysis) that the most significant physiological events take place. Some days before ecdysis,
much of the calcium in the shell is resorbed and stored in the gastroliths. At this time the shell
becomes quite compressible. Soon after, the membrane between the head and tail splits and
the crayfish begins the laborious task of extracting its entire body from the old shell.
Generally, the head and pereiopods are slowly exposed first, and then a sudden flick of the tail
completes the process. For some hours the moulted crayfish is very soft and vulnerable.
During this time water is absorbed into the body to assist in expanding the new shell before it
hardens. Once the shell is hard, this water is expelled leaving sufficient space for tissue
growth until another moult is necessary.
In newly hatched crayfish, moulting may occur every couple of days, however, as they get
larger moulting occurs less frequently and in adults of 100g or more, may only occur a couple
of times per year.
Because moulting is so physiologically demanding, death may occur at the time of ecdysis
even though the principal cause is unrelated. For example, crayfish stressed from poor water
quality will often die during moult due to the additional strain of the moulting process.
Growth data from crayfish under cultivation indicate that under ideal conditions, growth
accelerates from hatching to around 20g, it then remains reasonably constant to a weight of
between 50 and l00g and then slows increasingly up to the maximum size in excess of 200g.
An indication of growth can be gauged from examination of the size frequency of a large
sample of crayfish from a natural population. Figure 9.8 illustrates the size structure of a
population of C. quadricarinatus (males only) in a large waterhole near Walkamin, in May
1988. Three distinct modes can be distinguished, which correspond to three year groups or
ages; 0+ are those crayfish spawned from the previous summer.
Assuming that the bulk of spawning occurred around October/November, these crayfish are
approximately 4 to 5 months old, with an average size of approximately 70g. The next age
group, 1+, are those crayfish spawned from two summers previous. These crayfish have an
average size of approximately 110g at an age of 1.4 years. A third group 2+, which is less
clear, is likely to represent more than one age group of crayfish over 2 years old. The largest
of these crayfish, over 200g, may be 3 to 4 years old, however, this is likely to be the oldest
that the crayfish achieve in this population.
Progression from an assumed October spawning to the first peak (0+) indicates rapid
growth of 70g in 4-5 months. However, progression to the second peak (1 +) over a further 12
months indicates growth to only 110g. The reduced growth rate during the cool winter months
94
is responsible. This growth pattern adds further support to the . suggestion (Chapt.7) that a
considerable advantage can be achieved by rearing juveniles during winter and stocking them
for growout at the beginning of summer (September).
9.8
Feeding:
The array of appendages involved in selecting, manipulating, processing and ingesting food
for the crayfish is quite remarkable. Feeding is clearly not simply a process of food being
selected by the large claws and then transferred to the mouth. No fewer than 10 pairs of
appendages may be involved, enabling considerable discrimination in the selection of food.
Initial detection involves the antennae and antennules with which potential food items can be
located. As potential food items are approached, the first 3 pairs of pereiopods probe the
sediment seeking these items out. Material is then transferred by the chelae (claws) to the
mouth where several layers of appendages further sort and manipulate the food. Undesirable
particles can be eliminated and acceptable ones ingested. Although much of the food of C.
quadricarinatus is in the form of tiny particles, larger food items can be handled and shredded
before ingestion.
Once food has passed through the mouth it is transported through a short oesophagus to the
foregut (Fig.9.9), which is very muscular and equipped with hard teeth and grinding plates.
Food is chewed and semi-digested here with the aid of digestive enzymes secreted by the
hepatopancreas (digestive gland). Further digestion and absorption of nutrients takes place in
the midgut as well as separation of indigestible materials, which are pushed by muscular
action into the hindgut and then excreted via the anus beneath the tail fan.
Figure 9.8. Size frequency distribution for male Cherax quadricarinatus from a natural
population near Walkamin. Sample represents 141 crayfish captured in May, 1988. Age
groups recognised include 0+, 1+ and 2+.
95
Figure 9.9. Diagrammatic illustration of the alimentary canal of Cherax
quadricarinatus.
The food eaten by C. quadricarinatus under natural circumstances is mostly decaying plant
and animal material, collectively termed detritus. Bacteria and fungi associated with the
decomposition process are nutritious and particularly high in protein. It is not necessary for
this crayfish to consume animal material to obtain a protein supply. Crayfish maintained in
artificial tanks where the natural detrital food material is unavailable will not grow well. It is
possible that in time an artificially formulated diet will be produced which will enable
effective tank growout of C. quadricarinatus. However, none of the currently available
formulated feeds, including chicken, prawn or fish pellets, produce good growth in tanks. Use
of these feeds in ponds does produce reasonable growth, but the results of feeding trials
(Chapt.5) suggest that they may not be necessary.
9.9
Respiration:
Crayfish breathe by passing water over the gills from which oxygen is removed. The gills are
situated on either side of the body beneath the carapace and consist of feathery filaments
richly supplied with blood. Water movement over the gills is generated by a bailer appendage
near the mouth, the beating of which draws water under the edge of the carapace at the base of
the legs, upwards through the gill chamber and then forward and out on either side of the
mouth.
While in water, C. quadricarinatus can breathe normally at dissolved oxygen
concentrations as low as 1 ppm, however, to maintain healthy crayfish and ensure
maximum performance, they require 5ppm or greater. When removed from water, respiration
slows and tissues are fed through a different physiological system. C. quadricarinatus can
continue to respire and live out of water, under cool moist conditions, for considerable
periods. Consequently transportation of crayfish should involve adoption of these conditions.
Large numbers of crayfish held in small volumes of water will continue to respire normally,
using up all available oxygen quickly and death will ensue through suffocation.
96
9.10 Behaviour:
There are several aspects of C. quadricarinatus behaviour which are of particular interest
and/or significance to an aquaculture perspective. These are activity pattern, burrowing,
aggression and response to current. C. quadricarinatus is basically a nocturnal creature. It is
quite likely that two peaks in activity occur during each 24hr period, the first shortly after
dusk and the second just prior to dawn. Although this pattern is partly controlled by an
internal biological clock, it is the level of light which provides the greatest stimulus. This
explains the reduction in activity, and trap catch rates, during periods of full moon. Similarly,
activity in very clear water may be less than in turbid water through which less light can
penetrate. The level of activity is also closely related to water temperature. At the extremes of
the species temperature tolerance, activity will be reduced and naturally growth will also
decrease.
Burrowing behaviour of crayfish has received considerable attention, mainly because the
yabby, Cherax destructor, is capable of digging very deep burrows and destroying the
integrity of dam walls (Frost, 1975). There is considerable evidence which suggests that this
behaviour represents a survival mechanism, enabling this species to hibernate over dry
periods when water holes disappear (Lake and Sokol, 1986). It would not be surprising
therefore if C. quadricarinatus displayed similar behaviour because of its obvious advantages
in the harsh environment inhabited by this species. Nevertheless, the only burrowing
behaviour observed both in ponds at Walkamin or in natural populations involved
construction of simple U-shaped tubes generally less than 5cm deep and approximately 25cm
from opening to opening (type 1a of Horowitz and Richardson, 1986). These burrows have
been constructed by both small and large crayfish, they are predominantly occupied by one
individual, although there is some evidence that male/female couples may utilize a burrow as
a breeding chamber. Although the purpose of burrowing is unclear, their incidence represents
less than 2% of the resident population of a pond or water hole and they are non-destructive to
dam walls.
One of the most desirable attributes of C. quadricarinatus in regard to aquaculture, is its nonaggressive nature. It is quite remarkable that this species, heavily armed with large, well
articulated claws, is quite passive. Other freshwater crayfish species are often characterised by
their aggressive territorial behaviour. By comparison, C. quadricarinatus can be maintained at
densities in excess of 100/m² without destructive interaction. Although interactions between
individuals are observed, they are not offensive nor indicative of territoriality. There is some
suggestion of a hierarchical pecking order, whereby larger individuals dominate available
shelters, however, this appears to operate passively. The adaptive significance of this nonaggressive behaviour may be attributed to the natural habitat of this species in which
populations become aggregated as water holes diminish in size during the dry season. Overt
aggression under such conditions would lead to poor survival and therefore a severely
reduced capacity to re-populate during more favourable conditions.
Many fresh water animals display a strong response to water current, in many instances
moving upstream against the flow. C. quadricarinatus displays this response, which under
natural circumstances may function to avoid being swept towards the sea and more
particularly, to downstream regions characterised by sand substrate which does not hold water
during the dry season. Upstream, in the headwaters, more impervious soils predominate, and
permanent water holes prevail. This behavioural response has considerable application in
regard to aquaculture harvesting techniques (Chapt.6).
97
10 AQUACULTURE POTENTIAL
Cultivation of aquatic organisms - 'Aquaculture', has a long history. According to McLarney
(1984), aquaculture has been practised in China for over 2,000 years and in excess of 500
years in Europe. Although relatively new to the Americas, aquaculture has been embraced
with some vigour as the channel catfish and crawfish farming industries exemplify. Similarly,
many South-east Asian and South American countries are relatively new to aquaculture and
yet they have significant prawn and fish farming industries. This development has not always
been to the benefit of all concerned. Excessive coastal land clearing, significant hydrological
changes due to water demand and severe impact on markets for wild fisheries are obvious
examples.
A common theme to much of the world's aquaculture is the availability of relatively cheap
labour and/or an extensive approach. Introduction of aquaculture to Australia has been slow
because labour is relatively expensive and high land prices generally preclude extensive type
operations. In addition, the transfer of foreign technology is not always appropriate to local
circumstances. Although some level of success has been achieved with oysters, salmon/trout
and penaeid prawns, their are no outstanding success stories in Australian aquaculture. A
major constraint on the development of marine aquaculture ventures has been limited access
to high quality water adjacent to available and suitable land. Additional constraints arise at a
biological level. Many species are very exacting in their requirements and intolerant of the
inevitable mistakes which occur from time to time.
Consequently, increasing attention has been paid by prospective investors to assessing new
aquaculture candidates to fully evaluate the likelihood of success. To an extent, these
investors are looking for the ideal aquaculture species, the potential success of which has
minimal constraints. After two years of biological assessment, during which considerable
development has occurred in the commercial industry, it is clearly apparent that C.
quadricarinatus is such an ideal aquaculture species. Although significant production has not
yet been achieved, it is worthy of note that a considerable level of development has occurred
in some 4 to 5 years. The potential for a successful C. quadricarinatus farming industry to be
established within the next 5 years is very real.
Establishment of a market for C. quadricarinatus faces no apparent obstacles. The existing
demand for freshwater crayfish in Europe is in the order of 7,000 tonnes per annum. Although
the South-east Asian and Japanese markets are not entirely accustomed to freshwater crayfish,
the potential for developing a market their is very good, particularly in consideration of the
ease with which C. quadricarinatus can be transported alive.
This species achieves a substantial size, is attractive in colour and form, has a good flesh
recovery rate and compares well in flavour and texture with the most sought after crustaceans.
From an aquaculture perspective, the biology of the species is exceptional. Its physiological
tolerance to extremes of environment is great, particualrly in regard to temperature, dissolved
oxygen and salinity. Growth is rapid and sufficient to achieve a commercially acceptable size
within 12 months. Feeding requirements are such that relatively cheap materials will enable
significant production. The species is comparatively non-aggressive and performs well at
densities of 5 to 10 per square metre. It displays behavioural characteristics which lend
themselves to efficient harvesting practises.
98
C. quadricarinatus may be induced to spawn with relative ease. Handling of broodstock and
incubation of eggs requires no specialised facilities or procedures. The larval stage is entirely
contained within the egg which is carefully nurtured by the maternal parent. The reproductive
capacity of the species is relatively high. Juvenile crayfish, although fragile, are resilient and
respond well to intensive nursery conditions with appropriate food and shelter.
At all stages of the aquaculture operation, crayfish can be handled without fear of damage or
retarded performance. Potentially serious disease problems have not been forthcoming.
Although naturally occurring pathogenic diseases have not be reported from commercial
operations, complacency in the area of disease prevention is not advocated.
A broad gene pool, reflected in the wide morphological variability described for this species,
is of potentially great value in regard to selective breeding.
Physical (including climatic) requirements for cultivation of this species are broad and nonrestrictive, as the successful C. quadricarinatus farms of south-east Queensland indicate.
The existing C. quadricarinatus farming industry is characterised by considerable variability
in approach. Providing there is open communication within the industry, this variability is
healthy and will expedite the development of the most appropriate technology. Results
generated by this study have direct application to commercial operations, and it is hoped that
they will be used beneficially. Nevertheless, they do not represent THE recipe for successful
C. quadricarinatus farming. It will be up to individual crayfish farmers to interpret the
information contained in this report and apply it as necessary. For information on the 'broad
approach' to crayfish farming the reader is advised to contact local crayfish farmers or
representative associations, and to consult relevant publications (Anon., 1980; FACT, 19811988; Owen and Bowden, 1986; Mills, 1989; Bishop, 1989).
99
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