Production of juvenile redclaw crayfish, Cherax quadricarinatus I. Development of hatchery. Производство молоди АККР.

Aquaculture
ELSEVIER
Aquaculture 138 (1995) 221-238
Production of juvenile redclaw crayfish,
Cherax quadricarinatus (von Martens)
(Decapoda, Parastacidae)
I. Development of hatchery and nursery procedures
Clive M. Jones
Freshwcrter Fishertes md Aq~ac~lt~re
Cmtre, Department
ofPrimary
Industries, Research St&m,
Walkmnin,
Qld. 4872. Australicr
Accepted 8 April 1995
Abstract
Procedures
were developed for the controlled production of juvenile redclaw crayfish, Cherux
in tanks over two seasons. These included broodstock handling methods and involved
the definition of an in vivo ovary staging technique which permitted recognition of immature, maturing
and mature females. Hatchery techniques were also defined which demonstrated that male:female
ratios of up to I:4 were equivalent for successful mating and spawning. Up to 97% of females spawned
and carried eggs through to hatching when held in tanks at between 24.5 and 27.6”C mean daily
temperature and exposed to 14: 10 hours light:dark day length. A sequential series of seven egg stages
was defined from egg release through to hatching, based on morphological characteristics. The mean
duration of each stage was measured and cumulative statistics calculated, indicating a mean incubatory
period of 72. I days (range 47 to 84) and 66.3 days (56 to 71), respectively, for the two hatchery
runs. An exponential function was calculated which defines the relationship of fecundity and female
size and which indicates that fecundity ranges from approximately 200 to 1000 eggs per female.
Nursery procedures were developed which indicate difficulties with using the floating water plant
Pistiu as juvenile habitat, and the benefits of using artificial shelters. Newly hatchedjuveniles
stocked
at between 980 and 1842 m*, and fed a combination of formulated flake food and fresh zooplankton,
survived well (mean 52%) and increased in size by between 500 and 900% over 28 to 50 days. The
research demonstrates that C. yuudricarinutus
can be easily bred in captivity and juveniles reared
successfully with relatively simple facilities and techniques.
quudricurinatu.s
Kevword.c
Chrrax qurrdricarinutus;
1995 Elsevier Science B.V.
SSDI cfi0044-84X6(95/00068-2
Hatchery production; Nursery production; Culture methods - crustaceans
222
C.M. Jones /Aquaculture
138 (1995) 221-238
1. 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 ofAstacus
astucus 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, 1979b; 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, dependent to some
extent on the nature of the species being cultivated. Hatcheries have been used, but generally
to the extent of producing egg-bearing females which are stocked to grow-out ponds.
Intensive production of egg-bearing females or of juveniles, in the cultivation of Cherax
quadricarinatus, has been considered unnecessary. This species has a broad reproductive
season which may extend for more than 6 months, it may breed successively throughout
this season and has a relatively large reproductive capacity. Successful and sufficient production of juveniles has been achieved by maintaining reproducing populations of C.
quadricarinatus in earthen ponds, from which the juveniles are periodically harvested. The
most common practice is to distribute bundles of plastic mesh (onion-bag type material)
throughout the pond. Juveniles make use of these ‘shelters’, 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, production is unpredictable and growth is extremely variable.
As the redclaw aquaculture industry develops, it is likely that more managed and predictable production will become increasingly important. 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,
maintain egg-bearing 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 predatory aquatic insects
which inhabit grow-out ponds.
Preliminary information necessary to address these objectives was available in the literature. Studies of the reproductive biology of various freshwater crayfish provide useful
information on maturation physiology, mating behaviour, egg laying and incubation processes and post-hatching aspects (Hopkins, 1967; Mason, 1970a, b, 1977, 1978; Morrissy,
1970, 1975; de la Bretonne and Avault, 1977; Pippitt, 1977; Ameyaw-Akumfi,
1981;
Bechler, 1981; Lahti and Lindqvist, 1983; Woodlock and Reynolds, 1988a). In addition,
CM. Jones /Aquaculture
I38 (1995) 221-238
223
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.
Hatchery techniques applied to lobsters, Homarus (Chang and Conklin, 1983), freshwater shrimp, Macrobrachium rosenbergii (Aquacop, 1983; Malecha, 1983) and various
species of freshwater crayfish (Cuellar and Coil, 1979; Nelson and Dendy, 1979a, 1979b;
Keller, 1987; Trimble and Guade, 1988) were considered in designing a system suitable
for C. quadricarinatus. Similarly, juvenile rearing procedures employed for M. rosenbergii
(Stern et al., 1976; Malecha, 1983; Mulla and Rouse, 1985) and other freshwater crayfish
(Mason, 1978; Nelson and Dendy, 1979a, 1979b; 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 described.
Some of this information has previously been released in the report by Jones ( 1990).
Due to the inaccessibility of that report, the information has been reformatted for publication
in this journal.
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) in northern Australia ( 17.1 “S, 145.5”E).
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 (Vallisneria)
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 ovary staging technique. These females were dissected to determine the accuracy of the technique.
Male and female crayfish were selected randomly from 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 building with floor space sufficient to incorporate six
2.0 m diameter fibreglass tanks. Each tank was provided with a 5 mm depth of fine river
sand and various lengths of PVC pipe as shelter. Water was sourced from a bore and
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CM. Jones /Aquaculture
138 (1995) 221-238
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. Flow-rate was
adjusted to maintain an exchange of 100% twice per day. Depth was maintained at approximately 40 cm. Continuous compressed air aeration was provided in each tank.
The bore water was characterised by a constant year-round temperature of 25 to 26°C.
This temperature was 5 to 10°C warmer than the ambient water temperature of the broodstock tanks and the collection site at the time of initiating the hatchery procedures (JulyAugust). Fluorescent ceiling lights were connected to a time switch which enabled 14: 10
h 1ight:dark photoperiod, providing an additional 3 to 4 h 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 at the broodstock selection site.
Selected broodstock were introduced to the hatchery tanks over 24 h 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), representing total densities of
8.9, 6.7 and 6.0 crayfish per m2, respectively.
Crayfish were maintained in these tanks on a diet consisting primarily of Vallisneria
weed. All females were checked regularly (2-3 times/week) and berried individuals were
transferred to 80-l 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 fibre-plank walls.
Dimensions were 1 m high by 1 m wide by 25 m 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 60 cm and the water surface was covered
with the free-floating aquatic plant, Pistia stratiodes (water lettuce). The water depth was
sufficient to leave about 10 cm of free space beneath the root system of the plants.
Berried females 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.
C.M. Jones/Ayuaculture
138 (1995) 221-238
225
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.
The tank water was siphoned through a fine mesh screen.
1989 production
Based on the previous years experience and the completion of further experimentation
(Jones, 1990; Jones, 1995)) hatchery/nursery
procedures during 1989 were improved and
streamlined, although otherwise were similar to those described above.
Broodstock
The majority of broodstock were gathered from a ‘broodstock’ pond at the Freshwater
Fisheries and Aquaculture Centre, which had been stocked with 1988 broodstock crayfish
and considerable numbers of wild stock (Mitchell River Stock). Those gathered were held
in concrete tanks for a quarantine period of one 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, i.e. 6.4/m’. 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 increased by the installation of aquarium heaters to each
tank. These resulted in a 1 to 2°C increase over that in 1988. Light regime was maintained
at 14: 10 hours L:D.
Fresh Vallisneria weed was provided weekly in sufficient quantity to provide excess
food. Barastoc (TM) 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 just prior to egg hatching. Individual
stage duration was therefore not determined, although total incubation period was. Females
thought to be nearing egg hatching 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 condition were defined and recorded weekly for all unberried females.
Nursery
Nursery facilities were based on the results of previous juvenile nutrition/habitat
experimentation (Jones, 1990; Jones, 1995). Sixteen fibreglass tanks, 1.8 m by 1.0 m, 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 5 mm of fine river
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CM. Jones/Aquaculture
I38 (1995) 221-238
sand and equipped with 2 shelter types to maximise surface area and available edges, as
suggested for juvenile Macrobrachium rosenbergii (Smith and Sandifer, 1979). The first
consisted of fibreglass fly-screen mesh strips, 3 cm 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 juvenile M. rosenbergii.
Each unit consisted of a timber frame 100 cm by 30 cm by 30 cm, with 3 cm 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 30 cm.
Berried females of a similar late stage of egg development 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 zooplankton harvested from earthen ponds, and a
formulated flake diet (Frippak). Zooplankton consisted primarily of cladocerans (M&a
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 0.3 g 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 2-mm 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 mg. Differences among tanks
were then investigated using analysis of variance, and means comparisons were made with
Duncan’s multiple range test.
3. Results
1988 production
Broodstock
A non-intrusive in vivo ovary staging technique was developed for staging crayfish prior
to their selection for the breeding tanks. Using a concentrated fibre-optic light source, and
viewing anteriorly into the cephalo-thoracic
chamber, macroscopic features of ovarian
development were discernible. Subsequent dissection of 70 staged individuals enabled
CM. Jones/Aquaculture
Table I
Ovary stages of Cherux quadricarinattrs
recognisable
138 (1995) 221-238
221
by an in vivo staging technique
Characteristics
Ovary stage
Ovary stage number
No ovary discernible
Ovary visible, individual ova not discernible
Ovary clearly visible (olive green), individual
Immature
Maturing
Mature
1
2
3
ova apparent
confirmation and clarification of features observed in vivo. Three stages of ovarian development were recognised (Table 1) .
Using this technique, only maturing or mature females were chosen for the hatchery.
Between 27 July and 7 October 1988, 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 July to 2 December 1988, 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 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. la. A major proportion of individuals spawned within a period 2 to 4 weeks after
being introduced to the hatchery.
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. Females bearing eggs seldom had sperm remaining,
suggesting that the spermatophore persists for a few days at most.
Weeks
Fig. 1. Percentage frequency of spawning of female Cherux quadricarinatus at weekly intervals after exposure to
increased temperature and photoperiod within a controlled environment hatchery. 1988 (a) and 1989 (b) production seasons.
CM. Jones/Aquaculture
228
138 (1995) 221-238
Table 2
Morphological characteristics and duration (days) of successive stages of fertilised egg and larval development
for Cherax quadricarinarus (Mitchell River Stock), during incubation, at 25-26°C
Egg stage
Morphological
characteristics
of egg
Olive green, elongated
Dark brown, rounded
Yellow/orange
Red, eyes not visible
Red, eyes visible
Red, eyes and pereiopods visible
Egg hatched but juvenile still attached
to pleopod
Mean duration
(days)
se.
Maximum
Minimum
n
3.6
1.6
4.1
2.7
2.7
7.0
10.3
22
8
19
12
14
26
45
4
3
3
4
43
11
38
26
17
67
71
14.0
6.0
10.2
7.2
4.9
14.3
23.7
1
2
5
At egg release (stage 1) , eggs were olive green, opaque and approximately 2 mm long
and 1 mm wide. Distinct colour changes and other morphological developments were
evident as incubation progressed. Seven discrete stages were recognised and their mean
individual duration estimated from the observations made (Table 2). In addition, where
observations were less frequent, the interval between non-successive stages was recorded,
providing a schedule of cumulative development time (Table 3).
Over the period of hatchery production, 26 crayfish aborted their eggs (15.6%) and 1
mortality occurred. One hundred and forty individuals (83.8%) completed their incubation.
Nursery
Berried females were introduced to the nursery tank over a 60-day period beginning 16
September and each was removed after the release of young. Based upon fecundity estimates,
an estimated 45 000 juveniles were stocked. Harvesting took place on the 6 December.
Approximately 6000 ( 13.3%) juvenile crayfish had survived and were removed, of which
the majority were 0.4 g ( f 0.02 g). There were about 200 juveniles in excess of 2.0 g.
Harvesting was extremely laborious. Individual Pistia plants required dismembering to
ensure that well hidden juveniles were not overlooked. Organic debris, consisting primarily
of fine root hairs, had accumulated on the tank bottom, making siphoning of the tank water
very difficult.
Table 3
Cumulative stage duration (days) in egg development of Cherar quadricarinatus during incubation at 25-26°C.
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
Statistic
Mean
s.e.
Maximum
Minimum
n
Egg stage interval
s to 3
s to4
s to 5
S to 6
s to 7
Total
16.1
4.2
24.0
10.0
48
26.9
4.7
34.0
16.0
66
33.0
5.2
42.0
20.0
29
35.1
3.3
45.0
30.0
65
49.6
8.8
72.0
34.0
82
72.1
7.5
84.0
47.0
56
CM. Jones/Aquaculture
138 (1995) 221-238
229
1989 production
Broodstock
Broodstock were removed from the pond in early May. Ninety-six females were selected
for the hatchery ranging in size from 49.5 to 166.0 g and all of ovary stage 2 or 3 (Table 1) .
Hatchery
All crayfish were introduced to the hatchery tanks on the 29 May 1989. First spawning
occurred 2 weeks later, although only 3 crayfish had spawned up to the fourth week
(Fig. 1b) . Thereafter, spawning frequency was reasonably consistent, so that after 10 weeks,
85% of all broodstock had spawned. The hatchery was shut down on the 21 September
1989 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 7 1 days
with a mean of 66.3 days. There was little variability in incubation period between individuals. Water temperature in the hatchery ranged from a mean minimum of 245°C to a mean
maximum of 27.6”C.
A clear sequence of development in pleopod appearance was discernible 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 thoroughly so
that they resembled those of a newly moulted individual. The mechanism enabling this was
not clear, however, it certainly did not involve moulting as the intact carapace tags confirmed.
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.
Egg number appeared to be relatively reduced at stage 6, presumably due to mortality of
the larvae approaching their first moult. A predictive function for fecundity was therefore
generated (F = 12.7, P < 0.001, r2 = 0.56) for stages 1 through 5 only, representing the first
half of the incubatory period (Fig. 2) ;
log,,egg
number = 1.899 X (log,,carapace
length) - 0.466
Nursery
Seventy-three berried females were stocked to the nursery tanks from 10 August to 21
September 1989. 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 4).
Numbers of juveniles stocked to each tank were estimated from the fecundity function
described above, and ranged from approximately 1700 to in excess of 3500. These represent
stocking densities of between 1000 and 1800 per m2.
Feeding was initiated with 10.0 g (wet weight) of zooplankton and 1.0 g of flake daily.
This represented a feeding rate of 22.5% and 2.2% of stocked biomass, respectively. 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.
230
CM.
Jones /Aquaculture
138 (1995)
221-238
800
600
‘“:L
40.0
(4%)
1
45.0
50.0
Carapace
55.0
Length (mm)
60.0
(1409)
Fig. 2. Relationship between egg number and carapace length (mm) of Cherax quadricurinatus.
Egg counts were
made of the external egg mass (‘berry’) at egg stage l-5 (n = 12), representing the first half of the incubatory
period.
Final feeding rates prior to harvest 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
22.1”C, respectively. pH ranged from 7.6 to 7.9. Due to the high exchange rate, water quality
problems were not encountered.
Table 4
Production statistics for nursery phase of Cherm quadricarinatus
fed a combination of zooplankton and a prepared flake diet
Tank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
I.5
16
Release date
24/8/89
5/ 10189
819189
819189
13/9/89
13/9/89
21/9/89
IO/IO/89
lo/lo/89
3/10/89
3/10/89
15/10/89
2719189
15/10/89
13/9/89
2119189
Number
stocked
Density
( n/m2)
Harvest date
1784
3315
2173
1860
1831
1911
2466
3121
2391
2084
2326
2596
2677
2311
2119
1764
991
1842
1207
1033
1017
1062
1370
1734
1328
1158
1292
1442
1487
1321
1177
980
13/10/89
16/11/89
17/10/89
16/10/89
17/10/89
20/10/89
27/10/89
8/11/89
16/11/89
15/11/89
15/11/89
15/11/89
8/l l/89
S/11/89
23/10/89
23/10/89
reared in tibreglass tanks, at 22. I-25.7”C.
Period
Harvest
(days)
(n)
Mean
size (g)
Survival
(%)
50
42
39
38
34
37
36
28
37
43
43
30
41
23
40
32
660
144
687
1016
779
914
1756
1057
888
177
1326
2183
1401
1320
1280
1100
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
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
and
CM. Jones/Aquaculture
231
138 (199.5) 221-238
0.5
0
10
20
30
40
50
60
Time (days)
Fig. 3. 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) = 0,022,x e(o.05561
XaS(daYsl)~
1001
0
1
20
Percent
40
60
80
100
Frozen Zooplankton
Fig. 4. Relationship between survival and proportion of zooplankton
of nursery growth of juvenile Cherux quudricarinatus.
in diet which was frozen. Based on results
Periodic sampling of tanks provided mean size at time data which were incorporated with
mean harvest weight data to generate a growth plot (Fig. 3). Growth of juvenile crayfish
was successfully explained by an exponential function of the form;
weight (g) =0.0221 x e(O-OS.561
Xage(days))
The spread of data in the growth plot (Fig. 3) suggests considerable variability in growth
between tanks. This was also reflected in the variability between tanks in survival and mean
size at harvest (Table 4). Two tanks performed particularly poorly and were excluded from
the analyses. These were tanks 2 and 10 which suffered from a sudden and heavy infestation
of Corixid bugs (‘water-boatmen’).
It is assumed that these predatory bugs (Williams,
1980) were inadvertently introduced with the fresh zooplankton. Survival in the other tanks
ranged from 31.6 to 84.1% with a mean of 52%. There were no clear reasons for the
mortality, and it was attributed to natural processes.
232
C.M. Jones/Aquaculture
138 (1995) 221-238
Table 5
Mean daily growth index (mg) statistics and ANOVA results for juvenile Cherux quadricarinurus reared under
intensive nursery conditions. Tanks 2 and 10 excluded. Means sharing the same letter are not significantly different
(P<O.Ol)
Statistics
Daily growth index
Pairwisecomparison
n
Tank
Tll
T7
T12
T5
T16
T8
Tl
T15
T6
T3
T14
T4
T9
T13
2.5
a
65
4.3
b
74
4.5
b
75
4.9
b
71
5.3
b
70
6.0
b
84
6.1
b
67
6.3
b
92
6.4
b
65
6.8
b
55
8.6
c
68
9.7
c
96
9.9
c
56
10.4
c
86
0.5
0.4
0.3
0.2 1
0.1
(a)
.
.
’
I
I
f
5
- 0.5
Gl
0.4 :
3‘6 0.3
z 0.2
0.1
(b)
:.
I
,__ t
r
0.5
0.4 E
I
*
0.3 1
0.2
I
0.1
0
7
14
1
21
Age
I
’
28
35
03
42
(days)
Fig. 5. Mean weight (g) 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. Tanks chosen represent the range of harvest mean weight and survival. Tank 11 (a), tank 9 (b)
and tank 13 (c).
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. 4). There was
no equivalent correlation with growth.
Growth, expressed as the daily growth index, was significantly different between tanks
(P < 0.01) . Means comparisons (Table 5) indicate 3 reasonably well demarcated groups.
(i) Tank 11 with a low growth index value of 2.5, (ii) tanks 1,3,5,6,8,12,15,16 with growth
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.
CM. Jones/Aquaculture
138 (1995) 221-238
233
There was also considerable variability in growth between individuals within each tank.
Fig. 5 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 would
also contribute. In crayfish as young as 42 days, there may be as much as a 40% difference
between the smallest and largest individuals. Over a full grow-out period, this sort of
difference may be commercially significant. There is clear value therefore in researching
the genetic base of such variability with a view to selective breeding (Jones and McPhee,
1993).
4. Discussion
Procedures and facilities necessary to successfully hold broodstock, stimulate spawning,
incubate eggs and grow juveniles of C. quadricarinatus
were found to be simple and
straightforward. Production achieved was comparable to, or in excess of that documented
for other freshwater crayfish species.
While ovary staging proved to be reasonably straightforward and reliable, its effectiveness
in gauging the proximity of spawning was not particularly good. Accurate in vivo identification of mature ovaries may be an advantage in maximising of spawning success, but it
appears to contribute little to synchronisation
of spawning. Recognition of discrete macroscopic ovary stages has been previously documented for a freshwater crayfish (de la
Bretonne and Avault, 1977), although an in vivo method has not been previously described.
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 clarkli spawned under similar conditions
(Trimble and Gaude, 1988). Under more natural conditions, without artificial stimulus,
Pursiainen et al. ( 1983) reported that 95% of femaleAstucus 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 two seasons 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% to 30%. Sex ratios
234
C.M. Jones/Ayuuculture
138 (1995) 221-238
of this magnitude have been successful in breeding A. astacus (Keller, 1987)) Austropotamobius pallipes (Woodlock and Reynolds, 1988a) and Macrobrachium
rosenbergii
(Malecha, 1983).
The cleansing of the pleopods prior to egg release is likely to involve a chemical process,
however, there was no macroscopic physical evidence of organs or glands which may
contribute to such a process. The glair or cement glands which are known to facilitate
spermatophore dissolution and pleopodal egg adhesion in the Astacidae and Cambaridae
(Stephens, 1952, Thomas and Crawley, 1975, Holdich and Lowery, 1988) have not been
identified for the Parastacidae. Given that sperm release and egg adhesion appears to be
similar in the Parastacidae, equivalent glands are likely to be present, and may have the
additional function of facilitating the cleaning of the pleopods prior to egg release.
The incubation period for C. quadricarinatus was intermediate to those described for
other crayfish species. de la 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; Hessen et al., 1987), the 66 to 72
days incubation of C. quadricarinatus is significantly greater. By comparison, the New
Zealand Parastacid crayfish Paranephropsplanifrons
incubates its eggs for 112 to 119 days
(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). Other studies of C. quadricarinatus have indicated quite
different colour changes through incubation (Sammy, 1988; King, 1993). This suggests
possible genetic differences between redclaw from different river systems, and more probably, differences caused by environmental factors.
The variability in colour between individuals and 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, particularly for different river stocks of C. quadricarinatus and their causes is warranted.
Fecundity estimates for C. quadricarinatus indicated that as for other crayfish species
(Hopkins, 1967; Morrissy, 1975; de la Bretonne and Avault, 1977; Mason, 1977; Trimble
and Gaude, 1988; Woodlock and Reynolds, 1988b), egg number is a function of female
size, and total fecundity (for eggs < stage 5) is in the range of 200 to 1000 eggs per female.
It is clear from this literature that considerable attrition of eggs may occur between the
release of eggs from the ovary and the hatching of young after incubation. Such attrition
was evident for redclaw.
In 1988, berried females were transferred to release chambers within a nursery tank.
Although this method was straightforward, it is likely to have stressed the females, because
of the close 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 for freshwater crayfish during
CM. Jones /Aquuculture
138 (1995) 221-238
235
which the young become progressively independent (Mason, 1977; Mason, 1979; Bechler,
1981; Cukerzis, 1986; Jonsson, 1987).
In 1989, berried females were released freely into the nursery tanks so that the processes
of juvenile release could operate more naturally. These females were only removed when
there was no evidence of associated young. This approach may have contributed to the
increased productivity over the 1988 trial.
Provision of nursery conditions in 1988 was based on the premise that juvenile C.
quadricarinatus utilised aquatic vegetation as habitat within stream environments. Use of
a living plant within this system was considered advantageous because of: (i) stabilization
of water temperature; (ii) absorption of nitrogenous wastes; (iii) provision of natural food
organisms associated with the plant; (iv) suppression of excessive light; (v) the spatial
complexity of the root system, providing a high carrying capacity. Although the low production and difficulties in harvesting associated with this system do not support its use,
inclusion of alternative living plant material in nursery systems may be worth further
investigation.
The wide variability in size of the juveniles harvested is likely to have significantly
influenced survival. The polarised size distribution suggests that the approximately 200
crayfish in excess of 2.0 g predated heavily on smaller crayfish as they were released from
the females above. The result also suggests that the Pistia provided insufficient or inappropriate food and shelter to prevent this from happening.
The nursery facilities provided in 1989 were quite different and based primarily on the
results of a juvenile nutrition/habitat
experiment (Jones, 1995). The most significant
characteristics were: (i) use of many small tanks ( 1.8 m*) to enable batching of in-coming
crayfish, so that each tank had juveniles of similar size; (ii) provision of artificial shelters;
(iii) frequent feeding with both fresh zooplankton and a formulated diet. Results were
considerably improved over the 1988 production and compare favourably with those documented for intensively reared juvenile crayfish.
Despite the positive results achieved, there were aspects of the strategy for which improvements were immediately apparent, suggesting that greater productivity may be possible.
The increase in survival using frozen zooplankton suggests that it should be used in preference to fresh. This advantage was attributable to the zooplankton being more accessible
in frozen form, because it settles to the bottom, while live zooplankton may have been
flushed through with the flow of water, and lost.
However, live zooplankton is likely to have some nutritional superiority (Eagles et al.,
1984)) and at a greater density may have produced a better result. Although juvenile crayfish
are known to have limited innate behavioural abilities suited to food location and capture
(Doroshenko, 1979; Cukerzis, 1986; Burba, 1987), personal observation of juvenile redclaw suggests they are adept at capturing live planktonic organisms. Thorough observational
studies will be required to clarify this. Regardless of what type of food is used, its accessibility can be increased by minimising the depth of the water in the system and thereby
increasing relative food density. Alternatively, if juvenile production was performed in an
earthen pond, zooplankton availability could be maximised through active management of
water quality, nutrient levels and organic inputs.
Although a range of stocking densities was employed in the nursery tanks, there was no
clear indication of an optimal density. Because juveniles occupy the shelters provided,
236
C.M. Jones/Aquaculture
138 (1995)
221-238
density is a three-dimensional
issue rather than two-dimensional as for adults. On this basis,
shelter is likely to be closely tied to carrying capacity and its configuration and abundance
are likely to have a significant influence on survival. Mason ( 1978) demonstrated improved
survival of P. Zeniuscdus with the provision of particular habitat. Of the two habitats
provided in this study, the ‘float’ type appeared to be preferred. Similar studies are justified
for C. quadricarinatus to evaluate optimal habitat requirements for juveniles.
Acknowledgements
I thank Chris Barlow for supervision of this research and constructive comment on the
manuscript. I am grateful to Les Rodgers, Paul Clayton and Karen Barton who provided
technical assistance. This research was supported by a Commonwealth Reserve Bank Rural
Credits Development Fund grant.
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