Experimental pond production of marron, Cherax tenuimanus (Smith) (Decapoda: Parastacidae)

Aquaculture, 16 (1979) 319-344 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

319

EXPERIMENTAL POND PRODUCTION OF MARRON, CHERAX TENUIMANUS (SMITH) (DECAPODA : PARASTACIDAE) N.M. MORRISSY Western Australian Marine Research Laboratories, (A us tralia) (Accepted

P. 0. Box 20, North Beach, 6020,

W.A.

20 January 1979)

ABSTRACT Morrissy, N.M., 1979. Experimental pond production of marron, Cherux tenuimanus (Smith) (Decapoda : Parastacidae). Aquaculture, 16: 319-344. Forty-two, 4-month pond trials were carried out on a large indigenous crayfish in southwestern Australia - a candidate species for commercial aquaculture. Since growth rate and density are inversely related in this species the aim was to establish an intermediate range of density giving commercially acceptable values of growth rate and biomass. Survival over 4 months averaged 80.5% (30.7-100%) and was independent of density in the range 2-15/m2; low values (two below 50%) were due to oxygen depletion from overfeeding. The complex relationship between mean individual weight gain/4-month trial and initial mean individual weight was described indirectly using Mauchline’s (1977) linear plot of log growth rate in length against initial length. A multiple regression equation accounted for 93.3% of the variability in log growth rate with 45.7% due to initial size, 40.6% due to seasonal water temperatures,‘6.1% due to initial density and 0.8% due to feeding rate. Similar transformations were used to relate statistically production and biomass change to initial mean weight. Growth, production and biomass schedules were constructed for the most favourable temperature area of the south-west. A mean weight of 45 g at a biomass of 2100 kg/ha was predicted for the end of the first year of life and 111 g at 3175 kg/ha for the second year. Wide variability in individual weights represents a marketing problem. Plant material (poultry and lucerne pellets, compost) was supplied at rates of up to 1.0 kg/m2 per 4 months as a substrate for detrital formation. Pollution from these materials generated limiting oxygen deficiencies.

INTRODUCTION

Intensive commercial pond culture of freshwater crayfish has been attracting increasing interest in Australia (Morrissy, in press). The Australian parastacid decapods comprise 109 species, in nine genera, including the largest species in the world (Riek, 1969). The marron, Cherax tenuimanus (Smith), the third largest species, is unique to south-western Australia and has a considerable market potential (Morrissy, 1976a). The largely detritivorous but polytrophic marron is the dominant species in south-western Australian rivers by virtue of its high biomass (Morrissy, 1974b), but because wild stocks of marron

320

support a popular sport fishery they are protected from commercial exploitation (Morrissy, 1978a). However, man-made ponds and the ubiquitous farm dam (Morrissy, 1970a, 1974a) may be used to breed and rear domestic marron for sale under State Fish Farming Legislation introduced in 1976. Field studies on local populations of marron in rivers, farm dams and large public reservoirs showed that the average sizes of l-year-old and older age groups of marron were inversely related to density (Morrissy, 1974b). In the ten-fold density range 0.1-1.5 individuals/m2, average time for growth to the State legal minimum size of 120 g varied from 14 months to over 3 years; biomass was of the order of 300-600 kg/ha; the highest biomass value so far recorded for an unfed (farm dam) situation is 1107 kg/ha. Early pond production studies were associated with intensive pond breeding and early rearing of juvenile marron, successfully carried out since 1969 at the Pemberton Fish Hatchery (Fig. 1) (Morrissy, 1976b). Further rearing 33c

Cape

Nature

‘e

\

‘PaL3 u

~sseltan

‘Margaret

3P!

Cope

River

Leeuwm

35O s-

Fig. 1. Localities in south-western Australia.

of the earliest three pond-bred year class cohorts for 15-27 months at densities up to 25/m2 gave much higher biomasses than in the wild of a promising commercial order of up to 3660 kg/ha. Although growth was expectedly poor, the then inexperienced feeding using commercial poultry pellets gave average size similar to those at lower densities in the wild.

321

The intensive rearing trials of early young (for about 4 months after parental release) provided some perspective on the stocking density of newly released O+year-old marron needed in a production rearing pond. Initial densities of 378-1310/m2 gave, density correlated, very low growth rates and poor survival, down to 20%, despite feeding and abundant refuge cover (Moirissy, 197613). For more favourable future results densities in a lower range of lo-loo/m2 were indicated from the survival--density relationship. The species’ potential for very high growth rate at low densities and for commercially acceptable biomasses at high densities suggested the further pond trials at intermediate densities described here. The two variables, growth and density, cannot be maximized at the same time (Von Neumann and Morgenstern, 1947) but an optimum combination could be sought. The aim was to decide whether an acceptably high biomass could still be produced with growth to a saleable size, say 60 g (a large commercial size in Europe, U.S.A. and elsewhere in Australia) or 120 g (the present Western Australian minimum legal sporting size), rapidly enough for a realistic yearly or, at the most, 2-yearly turnover of stocks. The initial stocking density would depend upon survival rate to the recovered density, e.g. at 3000 kg/ha and 60 g mean size, 5/m2. There were indications from previous work that the growth and survival rates and hence production (sensu Allen, 1951), for a given density could be significantly increased by more adequate feeding of stocks. Although marron occur over most of south-western Australia (Morrissy, 1978b), previous seasonal growth studies indicated that annual production at Pemberton would be lower than under the more favourable seasonal water temperature conditions occurring over the Cape Leeuwin-Margaret River Busselton coastalstrip (Figs. 1 and 2) (Morrissy, 1976a).

24-

x--x

*---a

lo8

*---.

L

I

I

I1

I

,

/*

4

I

I,

JFMAMJJASOND

Fig. 2. Mean monthly water temperatures at the Pemberton Fish Hatchery and near Augusta in the area most favourable for marron growth in the south-west.

322

METHODS

Trials All pond trials were completed during the period 1974-1978 at the Pemberton Fish Hatchery (Department of Fisheries and Wildlife, Western Australia). Each trial duration was 4 months in one of the following three annual periods, April-August-December--April (Fig. 2). Ponds Two types and sizes of drainable ponds were used: small concrete ponds (designated ‘A’ in the Results) with a sand flooring, of area 14 m2 (7 X 2 m) and mean water depth 0.45 m, and larger clay ponds (‘B’) with a compacted limestone flooring of mean area 115 m2 (12-14 X 9 m) and mean water depth about 0.75 m. Escape and interspecific predation were prevented by smooth vertical perimetral walls, wire mesh fences and overhead plastic mesh cages. Water supply The continuous water supply piped separately to each pond from the hatchery stream was typical in quality of brooks arising in the high annual rainfall (> 1200 mm), forested catchments of south-western Australia, i.e. neutral, low salinity, bicarbonate waters dominated by sodium and chloride ions, viz pH = 7.2, TDS = 150 mg/l, NaCl = 110 mg/l, Ca” = 5 mg/l. Water supply was at least 1 m3/h (except for short periods of critical supply during December-April trials) giving at least one ‘exchange’ every 6 h for the smaller or 3.5 days for the larger ponds, respectively. Oxygen Aeration and water column mixing was promoted for 1 hour twice daily during the dry, hot season December-April, using small air-lift systems initially (vertical 4-cm diameter, 0.3-m length PVC pipe with a small air stone at the lower end) and later “Aquacharger” giant airstones (Environmental Management and Design Inc., Ann Arbor, Mich., U.S.A.) or, in the B-type ponds, 0.75 H.P. electric pumps (Finsbury Industries Ltd., Woodville, S.A., Australia), operated by time switch. Spot oxygen checks were made with a Townson and Mercer DO/TEMP meter and probe (Townson Portable Systems, Brisbane, Qld., Australia). Continuous oxygen levels were recorded in one of the larger ponds near the floor at the central outlet by a Rustrak DO/ TEMP recorder and stirred DO probe (Gulton Industries, Manchester, N.H., U.S.A.).

323

Refuge cover Excess refuge shelter was polypropylene (Tanikalon, Taniyama Chemical Industries Ltd., Okayama, Japan) rope fibre units described in Morrissy (1976b), or short lengths of PVC water pipe or, later and most conveniently for larger marron, 2 X l-m sheets of corrugated plastic roofing material. Food Substrate added biweekly for eventual detrital food formation in a pond was commercial poultry laying pellets in earlier trials and later, after comparative tests, commercial lucerne (alfalfa) pellets. Trial comparisons were made with pellets supplied at 0.1, 0.2, 0.5 and 1.0 kg/m2 per trial. Some tests also compared these pellets with clover reduced in a commercial “Compostumbler” (Osborne Metal Industries Pty. Ltd., Perth, W.A., Australia) prior to addition. Compost was prepared from dried clover (SO%), cow manure starter (25%) and powdered limestone (25%) and fresh compost was usually added to a stagnant pond a week before trial commencement. Animals All marron employed in trials were from pond-bred, densely reared, hatchery stocks of the O+, or l+ age group (Fig. 3). A small percentage of l+year-old female marron carry spawn during the spring of the second year of life (mean 9.6%, range O--37.5%, in 12 pond populations); anecdysial spawners occurred in August-December trials, lowering the mean growth rate of a group. Initial and final mean weights for a trial group were estimated by converting individual eye orbit carapace lengths (O.C.L. cm), measured using a vernier dial caliper (Helios), to individual weights (g) using the formula W = 0.93 L2-’ (Morrissy, 1970b). The size frequency distributions of marron year classes are typically somewhat positively skewed (Fig. 3) (Morrissy, 1970b, 1974b) due to the much more rapid growth of a few size dominant, i.e. initially larger, individuals (N.M. Morrissy, unpublished results). For the trial groups, standard deviation (S.D.) was related to mean individual weight (to) as S.D. = 0.99 + 0.44 il, (r = 0.90, P< 0.001); the coefficient of variation (S.D./U)) declined with increasing size, below 0.5 at 15 g, towards an asymptote of 0.44. Production over a trial was calculated using the method of LeBlond and Parsons (1977). RESULTS

Summarized results of the 42 production trials are shown in the Appendix reordered from the actual time sequence of successive trials on the basis of

324

I

140.

-

.’ . :

pmstart 120

of a maximum

1

triaq

T

T

. 100

mean - s.d. 80

l-T

20 -L

i 4

0

L-

u+ years old trial

groups

Fig. 3. Size and age variation of marron increasing mean individual weight.

in

order

of

mean

weight

used in pond trials. Trials are arranged

in order

of

seasonal periods and, within these periods, initial density. Comparisons between contemporary trials will be referred to the Appendix by the trial number shown in the third column.

Food type The basis of feeding in all trials was the provision of, largely, plant material as a carbon base for detrital formation. Unless otherwise specified, food quantities refer to the total amount/m’ fed to a pond over a 4-month trial. Pond growth of epiphytic algae and deposition of organic matter from the water supply were uncontrollable elements and, although the sand or clay

325

bottoms of ponds were raked and flushed between trials, there was obviously the additional factor of carryover of fine detrital material. For example, an unfed control trial (33) showed appreciable values for marron production and biomass increase of about 33% and 25%, respectively, of the values for comparable trials (31, 32) where feeding was employed. Compost at 1.5 kg/m2 gave approximately equivalent results (20) to poultry pellets at 0.5 kg/m2 fed biweekly (22); compost left standing in a pond for 4 months before a trial (21) gave reduced production (75%). Compost prepared 4 months before a trial and added just before the trial (4) gave reduced production (55%) compared to poultry pellets (5). Addition of fertilizer (1 kg urea and 1 kg super-phosphate to a 14-m’ (A) pond) with the compost did not increase production (10, 11) although algal production was enhanced by the end of the week before the trial and pond flushing commenced (Table I). TABLE I Algal production in composted marron ponds Trial No.

Chlorophyll = &g/l)

Pheopigments bg/l)

O.D. at 430 nrnt

10 11*

42.8 16.0

47.0 133.7

45.6 107.2

TCorrected to a sample equivalent of 1 1. *Fertilized pond, see text.

The compost trials were included to provide an alternative, possibly cheaper, source of marron food than commercial pellets which cost $A O.llO.l6/kg. Earlier trials used poultry laying pellets containing about 10% meat meal, a likely source of immediate water pollution. Later ones employed luceme pellets after the latter had been shown to give somewhat more favourable results in terms of growth and production (31, 32). Comparative laboratory assays showed that after 1 month of solution luceme pellets gave three times more retrievable solids than poultry pellets and the organic content was enhanced to about three times that of the initial organic content (Table II). Food quantity Particulate detritus formation and decomposing leachates, with associated algal blooms in the larger, B-type pools subject to a lower flushing rate, produced heavy oxygen demands, as discussed later under the heading Pond Conditions. Therefore, the optimal food quantity had to be a balance between the favourable effects of increasing food, i.e. faster growth and reduced mortality, versus, at higher feeding levels, the overloading of the pond system with organic matter leading to lower survival due to oxygen depletion.

*Mainly as NH,

Retrieved solids after 29 days D.W.

7.71 7.15

36.0 9.8

0.80 0.34

Day 29

Initial solids D. W.

1.14 0.56

Day 20

11.34 7.76

2.38 1.28

Day 12

Total

3.16 2.16

5

Day

3.86l 3.42=

1

20.68 20.06

31.4 7.0

6.38 3.76

0.34 0.26

0.40 0.28

0.62 0.44

1.22 0.76

3.80 2.02

Leachate total solids’ total organic2 (g/l) (D.W.) B A

Day

Test:

194 77.6

21 3.2

30 14.1

37 39.6

81 16.6

253 4.14

69.0 66.0

0.92 5.2

3.4 7.6

8.7 9.2

29 10.0

27 37.2

Leachate: total phosphorous3 total nitrogen*4 (mg/I) B A

25 0.07

25 0.11

100 0.22

150 0.44

100 0.25

150 0.25

150 0.39

350 1.42

425’ 2000 o.936 12.5

Leachate colour Hazen units O.D. 320 nm6 A B

0.55 0.25

0.45 0.55

0.90 1.80

3.20 1.85

0.45’ 0.25’

0.40 0.30

0.30 0.15

1.00 1.55

0.80 0.80

0.35 1.95

Oxygen uptake solids7 leachate (mg/l/lO min) A B

Comparison of the leaching and decomposition properties of poultry pellets (A) and lucerne pellets (B) at 20°C in non-aerated distilled water (replaced on each test day). Initial concentration of test solids (40 g/l, bag weight) was approximately 50 times that for a feeding rate of 0.5 kg/m2 in a B-type pond over 4 months. D.W. = dry weight (105°C)

TABLE II $

327

During the cooler August-December trial periods the desirable feeding rate for older 0+ and 1+ year-old marron was between 0.5 and 1.0 kg/m’; poultry pellets gave much less favourable results at 1.0 kg/m2 than at 0.5 kg/m2 (12,13) due to both reduced survival and growth; the difference was not so marked with less polluting lucerne pellets (14-17) although accumulation of bottom deposits was noted at the end of.a trial at 1.0 kg/m2 (17). With compost, results improved up to a level of 1.5 kg/m*, equivalent to 0.5 kg/m2 of pellets (N-20). During the warmest trial period, December-April, 1.0 kg/m2 gave poor survival (49.5%), even with the highest density of feeding marron (15/m2), due to poor oxygen conditions (42). For newly released O+year-old marron a feeding rate of 0.2 kg/m2 gave growth to a desirable level of 5 g (39). Food-production ratio Part of the dry plant-based food material added to a pond was lost as leachate by flushing (Table II). Particulate matter remained uneaten by the end of the trial (buried in the sand or clay bottom, or too fine or otherwise unacceptable to the marron; e.g. trials 7,18-22 - % organic content = 2.9 f 1.6%, range 0.88-7.53). Additional food was also obtained through the water supply (see control trial 33). Therefore, the ratio F/P (Appendix) calculated here for this scavenging crayfish differs in meaning from the usual conversion ratio of food eaten to flesh gain calculated for pond fish fed to demand. High values of F/P during the cold April-August period indicated that feeding at 0.5 kg/m2 (4, 5) to seasonally inactive marron was excessive compared with about 0.1 kg/m2 (1, 2) (Fig. 4). High F/P values during the AugustDecember period of rising water temperatures were associated with old compost (21), oxygen depletion in a clay pond which was not cleaned before the start of the trial (S), or overfeeding at 1.0 kg/m2 (13) giving reduced growth

o+3 x” overfeeding

a old

X uncleaned pond

13 X overfeeding

Fig. 4. Food/production ratios (F/P). *Lucerne pellets, X poultry pellets, D compost (+ 3). Superscripts denote trial numbers for values of particular interest (see text).

328

compared to a 0.5 kg/m2 trial (12). In summer, higher values (24,25) were associated with the first use of newly constructed clay ponds. However, feeding at the highest rate of 1.0 kg/m2 during summer in a subsequent year, gave a low F/P value of 3.82 (42) which may have indicated underfeeding of the marron. Compost fed at the lowest rate in the August-December period obviously resulted in poorer production (18) compared with higher rates of feeding (19, 20). However, while the majority of F/P values were low during the warm December-April period, probably reflecting underfeeding at 0.5 kg/ m2 so far as growth potential is concerned, increased feeding at 1.0 kg/m2 overloaded the pond system reducing survival (42). Survival Mean survival for all 42 trials was 80.5% ? 14.0. Only two (25, 42) or 5% of trials showed less than 50% survival; in one, an early trial, lowered survival occurred in a new B-type (clay) compost-fed pond and in the other with overfeeding of poultry pellets, both during the warm December--April period. There was no significant relationship between initial density and overall survival (ts9 = 0.9, P > 0.05). In one trial (40) lowered survival (71.0%) was deliberately induced at the highest density (15/m2) by provision of inadequate shelter (two synthetic weed bunches, instead of 10 in an accompanying trial (41) which showed 89.5% survival). In the smaller A-type ponds, 10 weed shelters were provided at higher densities and five shelters at lower densities. In the larger B-type ponds excess numbers of small lengths of PVC piping were provided initially but in later tests 10 corrugated sheets (2 X 1 m) were used, greatly facilitating recovery of the man-on at the end of trial. In clear water, marron take refuge during daylight hours, thereby avoiding avian predation, and emerge to feed at sunset (Morrissy, 197413). Refuge cover can also be provided by turbidity which encourages daytime feeding as documented in farm dams (Morrissy, 1970a, 1974a). Stocks of larger marron in the clay ponds noticeably generated clay turbidity; under such conditions survival was 96.7% with no material refuge cover (7). There was no overall correlation between survival and feeding rate (ts9 = 0.2, P > 0.05) although cases of overfeeding could be associated with somewhat lowered survival as related previously. Similarly, type of food did not influence survival (V.R.,,, ss) = 0.99, P > 0.05). A slight increase in survival rates with the changeover from use of poultry pellets to lucerne pellets could have been due more to improvement in management of pond conditions with time - see later - (compost 75.5%; poultry pellets 79.8%; lucerne pellets 84.1%). There was no significant trend in survival rate through the successive sets of trials (t39 = 1.8, P > 0.05). Survival of early 0+ group marron was consistently higher in A-type (82.9%, trial 37, and 83.6%, trial 39) than B-type ponds (64.4, trial 38, and 64.5, trial 36) possibly due to inadequate recovery of these smallest sizes from the larger, more heterogeneous clay ponds. However, overall there was no sig-

329

nificant difference in survival rates between the A-type and B-type ponds, 81.7% and 78.6%, respectively, despite the lower flushing rate of B-type ponds (&, = 0.6, P > 0.05). Together with growth rate, survival rate (S) is the important variable’ influencing the production (P) over the trial period, the surviving production (P,) at the end of the trial, and most importantly for practical purposes, the change in biomass (AB) over the trial (AB = B4 -B, = P, - B, (1- S)); The relationship between AB/P and S was: AB/P = -2.28

+ O.O355%S

(n = 41, r = 0.64, P < O.OOl),

where %S = 64.2% when ABIP = 0 Taking the mean survival rate of 80.5% for a 4-month production period, an initial density of newly released young marron at lo/m2 would give the desirable surviving densities of 5/m2 or 2.5/m2 in 1 and 2 years, respectively, with some allowance for a lower survival rate (75%) in the first period. Growth Newly released O+year-old juveniles were usually available during the first half of January for inclusion in trials by mid-January (37, 38). Earlier breeding trials over 5 years showed that the annual release date at Pemberton was related to water temperature (Morrissy, 197613). Breeding trials at the warmer localities of Augusta and Margaret River, which are being recommended for marron farming, gave release of juveniles during November 1976 compared with the following early January at Pemberton. An earlier release was obtained at Pemberton in late 1977 by covering an A-type pond containing breeding stock with clear plastic sheeting and by using a minimal water exchange rate. The resulting elevated water temperatures (mean 17.4”C versus 14.O”C in an exposed adjacent pond) gave release of stock in early December for inclusion in the December-April trials (36, 39). The additional month under test conditions gave at least double the final mean weight of earlier trials without any reduction in survival to April. Turning to the growth pattern of larger marron, increase in mean individual weight, AZ, over the trial period can be shown statistically to have been most influenced by the initial mean weight of the marron, Go, and the trial season, i.e. presumably due to the usual relationship between the activity of poikilotherms and water temperature. The relationship between As and w,, featured an extremely steep ascending limb rising to a maximum value of A$ between Go = 10 and 20 g and a slowly descending limb for larger initial sizes (Fig. 5). For the warmest (December-April) period’ A; attained a maximum of approximately 39 g, for the August-December period about 15 g and for the coldest (April-August) period about 4 g. To facilitate graphical inspection of various transformations of the data prior to statistical - description of the complex A w/w o relationship, values for the two cooler

330

periods were multiplied by 2.6 and 9.75, respectively (Fig. 5). Although commercial aquaculture deals in weights of animals, and for that purpose body lengths - particularly carapace lengths - by comparison have little practical value, both measurement of individual size and statistical analysis of size relationships are more conveniently carried out in terms of the linear dimension. Using carapace lengths, a linear relationship was obtained between growth rate and initial size (Fig. 6), using the transformation suggested by Mauchline (1977). This allowed the complex relationship shown in Fig. 5 to be described indirectly by the usual methods of linear regression, and for extrapolation to larger sizes of marron to be made with some confidence. A highly significant multiple regression equation (FC4 ss) = 125, P < 0.001, R square = 93.3%) was obtained using the following variables: growth rate in

30- /

0

I

:I

25

El

I I. I

aw920_

a

x .;

x

I I 15- I lo IO lO-1. I I* 56 * 3 3

Fig. 5. The relationship between change in mean weight Aii~, and initial mean weight AGo, overa4-month trial.. April-August, AiirX 9.75; X August-December, A?? X 2.6; 0 December--April. Insert: The calculated relationship between mean number of ecdyses and initial mean weight over the December-April period.

331

71 0

,

I

I

1

2

3

!

&) cm"

,

5

Fig. 6. Mauchline’_ (1977) linear blot for growth rate against initial size. AT, change in mean O.C.L. cm; I,, initial O.C.L. cm. A and B are fitted regression lines using four and two determining variables, respectively (see text). -

-

the form of {log,, (AZ / lo) 5% } where A % and &, (cm) corresponded to A& and Eo, respectively; initial size, &, (P < 0.001, accounting for 45.7% of the variability in growth rate); the water temperature sum, temp-sum, over the trial period in “C-days (P < 0.001, 40.6%); the initial density, do as numbers of marron/m2 (P < 0.001, 6.1%); and the total amount of food material over the trial period, f, kg/m2 (P < 0.05, 0.8%); viz, log,, (Ai-&%)

= 1.014 - 0.4029 (&) + 0.0008752 (temp-sum) - 0.03061 (do) + 0.1654 (f)

332

However, values of A% derived from this equation, for prediction in formulating a growth schedule, appeared to underestimate both the growth of newly released O+year-old juveniles and the largest sizes of marron (Fig. 6, fitted regression line A). The simpler regression equation employing only the dominant factors of initial length and temperature sum appeared to be of more realistic predictive value for the larger sizes of marron (Fig. 6, line B; Fig. 5); viz, logl,(Ar/&)

= 0.5674 - 0.3192

(&) + 0.0009331

(temp-sum).

Relative to these variables, density in the range 3---15/m’ had a very minor influence on growth (c.f. trials 27, 31, 42; 12, 13, 23). In addition, a mean final weight of 5 g vvas employed for the first 4-month period, corresponding to observed values when early release of O+year-old marron was obtained by the method described at the beginning of this section. Values of A%,for a 4-month trial period represented varying number of ecdyses for the average individual depending upon the initial size. For an independent validation of the magnitude of the predicted AL%values, the mean number of ecdyses were calculated. Ecdysial increments were available for marron held under favourable laboratory conditions of isolation, heating (16-2O”C), regular feeding and aeration (Fig. 7). The increment increased to r.zr

I

frbm y= -0~22L4215x,

/I / /

/

/

’

/

Hiatts I

f

n=5% r=049&

plot of post-ecdysial on pre-ecdysial

O.C.L. (yl O.C.L. (Xl

/ y=0~110+1~056x,n=L6,r=O~9691

5

UI

0

’

i

‘9

‘,#‘,

20

Bodyweiht “0

60 60~00

3’011

9

l!O

9,.

200

3aO

4?0

!OO

%,“I

1 5 6 f a Oriitat tarapace length cm (0C.L.I Pre - ecdysial size

I

9

’

10

Fig. 7. Relationships between individual ecdysial increment and pre-ecdysial sipe for marron. Fitted mean relationship for laboratory man-on held under favourable conditions (see text). - - - Upper limit to all laboratory and field observations.

333

a maximum of between 0.9 and 1.0 cm O.C.L., or about 70 g (58%), with an apparent upper limit to all observations of 1.12 cm O.C.L., at about 5.5 cm O.C.L. or 123 g body weight. Hiatt’s plott (Hiatt, 1948; Kurata, 1962) of post-ecdysial O.C.L. on pre-ecdysial O.C.L. was used to obtain the relationship(s) between mean ecdysial increment and pre-ecdysial size (Fig. 7). The mean number of ecdyses represented by a predicted value of Aii~for a given value of Go were obtained by addition of successive ecdysial increments commencing at G, until the value of Aw was encompassed. The calculated ecdysial frequencies (Fig. 5, insert) showed reasonable agreement to observed values. Sampling of newly released O+year-old pond marron at frequent intervals indicated, from modal progression, completion of the first free-living ecdysis within 2 weeks (Morrissy, 1976b); in laboratory experiments, under the favourable conditions mentioned above, marron of 30 and 50 g ecdyse at about 2- and 3-months intervals, respectively (N.M. Morrissy, unpublished data). Growth schedules were calculated for various combinations of the three Pemberton trial periods (Fig. 8). The highest annual growth rate for a mean .l&~O”C /’

IL0

120 -

/ /*

/

?I/’ /

loo-

80-

1: 60 -

mean annual temperature

air

Cape Leeuwin - 16.8”C

Fig. 8. Predicted growth schedules using various combinations of Pemberton 4-month trial periods. 1, April-August; 2, August-December; 3, December-April.

334

annual air temperature of lS.O”C, equivalent to continuous December-April Pemberton conditions, is not achievable in any exposed pond situation, at least not in south-western Australia. This schedule is only of remote relevance, at the present time, for the highly idealized ‘battery’ stage of aquaculture where temperature and other environmental factors are controlled at optimum levels. However, the second highest schedule, for a mean annual air temperature of 16.4% should be achievable along the Cape Leeuwin-Busselton strip (Fig. 1) where the most equable annual air temperature conditions in southwestern Australia occur (Morrissy, 1976a). The available corresponding water temperature data support this conclusion (Table III).

TABLE III Temperature sums (“C-days) for three growing periods at marron farming localities (see Fig. 1). Apr-Aug

Aug-Dee

Dee-Apr

Mean annual temperature (“C)

Air’ Water2 (Fish Hatchery)

1478

1620

2188

14.5

1282

1619

2126

13.8

Cape Leeuwin

Air’

1863

1914

2339

16.8

Busselton

Air’

1620

1858

2390

16.1

Cape Leeuwin-Busselton mean

Air’ Water3 (Augusta ponds) Water’ (Margaret River marron farm)

1742 1880

1886 2356

2365 2723

16.4 19.1

2120

2289

17.1

Pemberton

1 1844

‘Climatic Survey (1965). *From monthly means of daily, max-min thermometer recordings. 3From monthly means of daily maximum and minimum surface and bottom recordings. ‘From monthly means of occasional readings at 9 a.m. and 1.5 m depth.

Production

and change

in biomass

The relationships of both production, P, and change in biomass, AB, to Go were similar to that for AZ and, therefore, were analysed similarly giving

335

the following log,,

multiple

regression

equations:

(@‘a/&) = 0.2148 - 0.2197 (&) + 0.0004088 (temp-sum) + 0.1376 (arcsin survival)

F (3,

= 184 (P < 0.001); R square = 93.7%; c accounted for 72.7% of the 37) variability (P < 0.001); temp-sum, 20.2% (P < 0.001); and arcsin survival, 0.9% (P < 0.05).

log,, (AI31’3/&) = 0.1089 - 0.2202 (&,) + 0.0004490 (temp-sum) + 0.2174 (arcsin survival)

F (3,

= 89 (P< 0.001); R square = 87.8%; &, accounted for 65.1% of the 37) variability (P < 0.001); temp-sum, 20.7% (P < 0.001); and arcsin survival, 2.0% (P < 0.05).

Schedules for cumulative production and biomass were calculated from these equations (Fig. 9), using a mean survival value of 80.5%, corresponding to the growth schedule shown in Fig. 8. LOG

300

$ .z v) % F 200’ g

loom

1 Men ths

Fig. 9. Production and biomass schedules corresponding to Fig. 8.

336

Pond conditions The December-April trials embraced the annual period of drought and of high air and water temperatures typical of the mediterranean-type climate of the region. The start of the trials in the summer of 1974-1975 occurred after a wet season of average rainfall but the succeeding 3 years were ones of increasingly severe drought. While the high water temperatures of the December-April trials favoured expression of the growth potential of the marron, the stored river water supply in this period was limiting both with regard to quantity for flushing ponds and, in the worst summer (1977-1978), to quality (low oxygen levels due to stagnation). Therefore, maintenance of favourable oxygen levels in the ponds was of primary concern. Previous experience had shown that gross overfeeding of marron in ponds shortly produced obvious catastrophic mortality and ‘walking out’ of shelving B-type ponds. However, feeding levels were sufficiently well judged in the present trials for no obvious mass mortality to be observed. Very poor survival occurred in only two December---April trials (25, 30.7%, new B-type pond fed compost; 42, 49.5%, A-type pond fed poultry pellets at 1 kg/m2, c.f. 41, 89.5%, fed at 0.5 kg/m2). The oxygen tolerance levels of marron for ecdysis, growth and feeding are unknown; laboratory experiments where oxygen levels fell below 70% at 20°C have shown reduced ecdysial increments. On a diurnal basis, lowered oxygen levels - in the early morning due to algal blooms or in deeper stagnant water over detrital sediments - could be avoided, for example for ecdysis, at mid-afternoon near a bank in the shelving B-type ponds. Although both types of ponds were quite shallow with surface area/volume ratios of 2.2 (A-type) and 1.3 (B-type), the deeper B-type ponds, with a lower exchange rate of water, showed a summer mid-afternoon temperature stratification from day to day. Despite overflow being drawn off from the bottom of the outlet stand pipe, vertical temperature differences of up to 5.75% were recorded in the 1 m depth of water near the outlet in the hottest month, February. Circulation of bottom water, early morning aeration, and ‘breaking up’ of algal blooms at mid-afternoon were attempted by three methods particularly during critical periods of poor water supply, for B-type ponds with a lower water exchange rate, and in cases of a heavier than usual feeding rate. Circulation of the water in a pond using a small electric pump was most effective (Figs 10,ll and 12) while the more traditional methods, air-lift devices and, later, giant air stones, produced no useful effect (Figs 11 and 12) possibly due to the shallowness of the ponds. DISCUSSION

A number of problems beset the development of commercially viable freshwater aquaculture projects on native Australian species such as marron (Maclean, 1975; Morrissy, in press). As yet only trout farming has been

337

.

I

I

/

(5.6%) Ciifculating

/for

pump

opsrofing

1 hour weother sunny windy

311

120Uhrs

’ 1

’

’

Dee 1976

weo fher sunny humid wine)

overcast no wind I

’

I

7600---P WOO

2 Dee

1976

I

-I____~ 1600

L

0900

I

1600

3 Dee 1976

Fig. 10. Typical diurnal changes in oxygen concentration in an organically overloaded B-type pond (trial 27). Flow, 2 m3/h; water temperature 19-22°C.

established, based upon an imported species and technology with the local market developed initially by imported farmed products. Marketable

size

A regional social problem is the expectation that aquaculture will provide ‘jumbo’ sizes of marron or at least the present amateur fishing size of 120 g because of the very large individual size to which marron may grow (“2 kg). There is also the expectation that the abundant wild stocks of undersized marron in the sport fishery will be protected from illegal plunder for sale by this common size limit. These expectations neglect consideration of mortality over the long growth time necessary to produce such sizes and the need for a commercially viable project with annual crops to operate on a l-year or, at the most, 2-year growth schedule to avoid more than duplication of growing ponds. The size requirement for the export market is around a mean size of 45 g which could be obtained in 12 months from, maternal release at 2100 kg/ha (Figs 8 and 9, second highest curve). Or, less efficiently, over 2 years 120-g and larger individuals could be produced for local marketing but these would be less than 50% of the crop of 3175 kg/ha. Therefore the viability of the developing industry will be severely restricted for some time by the local, legal requirement for 120-g or larger marron. Overseas marketing of the

338

. . .

.

2

r‘

. i b .

E

. .

E 8

zi

.

?j

.

c1

-* **

.

w

.*-

l

.c .

*. %

l

%

.

%

.

*

%b

l

y’ .‘.’

%.

c*

. .

u

*** *

.

. %

-

** %

.

**

*

Y

l

%

.

*.

z

**

% .

** % . ** *

.

339

24“c

\

22-

/* .-._. L SUPPlY 24~OT 3.8 mgf! 146%0 / 6 /. cloud cool.10

I =JPPtY 24.2’C 4.7mgp (57% 02)

21-

hot,

50

%

cloud

20 I

I

lEio0

hrs

I

I

I

I

I

8 March

I,

I

01.00

20.000 1978

,

,

,

,

I,

,

I

,

11.00

06RO 9

March

1978

Fig. 12. Maintenance of favourable oxygen concentrations in a B-type pond (trial 29), subject to poor quality water supply, using an automatic circulating pump. Flow, 1 m3/h.

smaller marron will require a long term commitment by the industry to production of a large, guaranteed, annual supply, a necessary condition of export contracts. Temperature The pond trials confirmed the unsuitability of most of south-western Australia for.efficient marron farming because of very low growth for at least 4 months over winter. The need for site selection in the Cape LeeuwinMargaret River-Busselton strip (Morrissy, 1976a) is re-emphasized. The strong moderating oceanic influence over this coastal extremity results in the warmest winter conditions in the south-west (Climatic Survey, 1965). More generally, this area shows minimal annual variation in temperature about a favourable level of mean annual temperature, conditions found elsewhere in Australia only on the northern coast of New South Wales (Climatic Averages Australia, 1956). Limitations of trial results The usual caution must be applied in extrapolating the present results from small, protected ponds maintained on an experimental basis and, in particular, cleaned every 4 months, to larger units maintained by initially inexperienced, private operators. The efficiency of this transition for proven

340

experimental agricultural yields in Australia can be as low as 60% (Davidson, 1969). Prevention of oxygen depletion appears to be a major worldwide problem for intensive aquaculture of bottom-crawling crustacea (e.g. Avault et al., 1975; Wickins, 1976; Green et al., 1977). A most serious limitation at present for establishing intensive commercial-scale crayfish farming ventures, or possibly improving experimental pond production, is the quantity of water required for flushing to prevent oxygen depletion due to food pollution (Goldman et al., 1975). In obtaining the present experimental results on marron, water supply was limiting at times in a most favoured rainfall locality (>1270 mm annually) because of the summer drought of the region. Except for these critical summer periods the minimal water supply rate of 1 m3/h for a B-type pond (86 m”) yielding 3000 kg/ha represents a yield per unit volume of water of only about 0.002 kg/m3; c.f. 0.003-0.005 kg/m3 for highly intensive trout farming and 0.04 kg/m3 for Mucrobruchium farming at a similar yield to marron (Shang and Fujimura, 1977). Obtaining this magnitude of water supply for a large hectarage of ponds is either impractical over most of south-western Australia or represents an unacceptable level of investment in surface storage for the dry season or in pumping from ground water. Development of the routine use of water circulation-aeration techniques is obviously necessary as has been found elsewhere where water supply is extremely limiting (Rappaport et al., 1976). The other obvious strategy now receiving research attention is use of a food base having lower pollution properties_ Most freshwater crayfish are now recognized as basically detritivorous (Momot et al., 1978), feeding by selective grazing on small microbially enriched particles. Preparation of a nutritionally complete food using a micro encapsulation technique to obtain extended water stability and fine particle size (Jones et al., 1974) appears to be one approach to the problem of preventing water pollution and consequent low oxygen levels. However, investigation of an array of plant materials for suitability as natural detrital substrates (Goyert and Avault, 1977) and reduced leaching properties appears to offer scope as a more immediate and less expensive means of improvement. Pre-leaching of material for 5 days before pond addition, is obviously a helpful technique (Table II). ACKNOWLEDGEMENTS

Pond trials were conscientiously maintained by Manager G. Cassells and Assistant A. Church of the Pemberton Fish Hatchery staff. Dr D.A. Hancock, Chief Research Officer of the W.A. Marine Research Laboratories, and P.L. Morrissy provided constructive criticism of the manuscript.

REFERENCES Allen, K.R., 1951. 10: 1-231.

The Horokiwi Stream. A study of a trout population.

Fish. Bull. N.Z.,

341 Avault, Jr, J.W., De la Bretonne, L.W. and Hunter, J.V., 1975. Two major problems in culturing crayfish in ponds: oxygen depletion and overcrowding. Proc. Int. Symp. Freshwater Crayfish, 2: 139-144. Climatic Averages Australia, 1956. Temperature, Relative Humidity, Rainfall. Bureau of Meteorology, Commonwealth of Australia, Melbourne, Vie., 107 pp. Climatic Survey, 1965. Region 16 - Southwest Western Australia. Bureau of Meteorology, Commonwealth of Australia, Melbourne, Vie., 93 pp. Davidson, B.R., 1969. Australia Wet or Dry? The Physical and Economic Limits to the Expansion of Irrigation. Melbourne University Press, Vie., 264 pp. Goldman, C.R., Rundquist, J.C. and Flint, R.W., 1975. Ecological studies of the California crayfish Pacifastacus leniusculus, with emphasis on their growth from recycling waste products. Proc. Int. Symp. Freshwater Crayfish, 2: 481-487. Goyert, J.C. and Avault, Jr, J.W., 1977. Agricultural by-products as supplemental feed for crayfish, Procambarus clarkii. Trans. Am. Fish. Sot., 106: 629-633. Green, J.P., Richards, T.L. and Singh, T., 1977. A massive kill on pond-reared Macrobrachium rosenbergii. Aquaculture, 11: 263-272. Hiatt, R.W., 1948. The biology of the lined shore crab, Pachygrapsus crassipes Randall. Pac. Sci., 2: 135-213. Jones, D.A., Munford, J.G. and Gabbott, P.A., 1974. Microcapsules as artificial food particles for aquatic filter feeders. Nature, London, 247: 233-235. Kurata, H., 1962. Studies on the age and growth of crustacea. Bull. Hokkaido Reg. Fish. Res. Lab., 24: l-115. LeBlond, P.H. and Parsons, T.R., 1977. A simplified expression for calculating cohort production. Limnol. Oceanogr., 22: 156-157. Maclean, J.L., 1975. The potential of aquaculture in Australia. Aust. Fish. Pap., 21: l-133. Mauchline, J., 1977. Growth of shrimps, crabs and lobsters - an assessment. J. Cons. Int. Explor. Mer, 37: 162-169. Momot, W.T., Gowing, M. and Jones, P.D., 1978. The dynamics of crayfish and their role in ecosystems. Am. Midl. Nat., 99: 10-35. Morrissy, N.M., 1970a. Report on marron in farm dams. Fish. Rep. West. Aust., 5: l-34. Morrissy, N.M., 1970b. Spawning of marron, Cherax tenuimanus (Smith) (Decapoda: Parastacidae) in Western Australia. Fish. Bull. West. Aust., 10: l-23. Morrissy, N.M., 1974a. The ecology of marron Cherax tenuimanus (Smith) introduced into some farm dams near Boscabel in the Great Southern Area of the Wheatbelt Region of Western Australia. Fish. Bull. West. Aust., 12: l-55. Morrissy, N.M., 1974b. Spawning variation and its relationship to growth rate and density in the marron, Cherax tenuimanus (Smith). Fish. Res. Bull. West. Aust., 16: l-32. Morrissy, N.M., 1976a. Aquaculture of marron. Part 1. Site selection and the potential of marron for aquaculture. Fish. Res. Bull. West. Aust., 17, Part 1: l-27. Morrissy, N.M., 1976b. Aquaculture of marron. Part 2. Breeding and early rearing. Fish. Res. Bull. West. Aust., 17, Part 2: l-32. Morrissy, N.M., 1978a. The amateur marron fishery in Western Australia. Fish. Res. Bull. West. Aust., 21 :‘l-44. Morrissy, N.M., 1978b. The past and present distribution of marron in Western Australia. Fish. Res. Bull. West. Aust., 22: l-38. Morrissy, N.M., in press. Aquaculture. In: W.D. Williams (Editor), An Ecological Basis for Water Resources Management in Australia. A.N.U. Press, Canberra, A.C.T. Rappaport, A., Sarig, A.S. and Marek, M., 1976. Results of tests of various aeration systems on the oxygen regime in the Genosar experimental ponds and growth of fish there in 1975. Bamidgeh, 28: 35-49. Riek, E.F., 1969. The Australian freshwater crayfish (Crustacea:Decapoda:Parastacidae), with descriptions of new species. Aust. J. Zool., 17: 855-918.

342

Shang, Y.C. and Fujimura, T., 1977. The production economics of freshwater prawn (Mucrobruchium rosenbergii) farming in Hawaii. Aquaculture, 11: 99-110. Von Neumann, J. and Morgenstern, O., 1947. Theory of Games and Economic Behaviour. Princeton University Press, Princeton, N.J., 641 pp. Wickins, J.P., 1976. Prawn biology and culture. Oceanogr. Mar. Biol. Annu. Rev., 14: 435-507.

7 8 9

10 11 12 13 14 15 16 17

18 19 20 21 22 23

3

5

15

6

4 5

15

(2

3

A A A A A A

A A A A A A A A

B B B

B

A A

B

1B 2 B

10

5

Season Approx. TrialPond initial No. type* density/m"

Summary of 4-monthmarrontrials

APPENDIX

0.098 0.074 0.066 1.83 0.47 0.092 1.35 0.57 0.55 1.5 1.5 0.5 1.02 0.47 0.97 0.47 0.97 0.51 1.02 1.53 2.34 0.51 1.00

LP LP

LP

C' PP

LP

C PP LP

C2 C PP PP LP LP LP LP

C C C C' PP PP

Type** Amount*** of of food food

130 -21 70

483, 462 483, 553

68 310 384 272 378 1047 2.24, 4.81 2.24, 6.17 2.24, 5.76 2.24, 4.84 2.24, 5.99 3.20,lO.g

343, 411 343, 653 343, 727 343, 615 343, 721 491,1538 55.7 69.0 82.4 82.9 78.6 92.4

441 432 583 270 496 723 613 524

3.20,13.0 164, 605 3.20,12.2 164, 596 3.20,15.0 164, 747 3.20,10.4 164, 434 8.77,23.6 448, 844 551,1274 8.77,22.1 29.0 ,41.0 1482,2095 27.0 ,37.8 1380,1904

5.11(0+) 91.4 5.11(0+) 88.6 5.11(0+) 97.1 5.11(0+) 81.4 5.11(0+) 70.0 6.28(0+) 91.9 5.11(1+) 100.0 5.11(1+) 98.6 15.3 (0+) 15.3 (O+) 15.3 (0+) 15.3 (O+) 15.3 (O+) 15.3 (O+)

226 439 -74 510

108, 334 453, 892 719, 645 1625,2135

5.48,lg.l 13.7 ,27.9 21.1 , 28.5 46.3 ,61.0

1.97(0+) 88.9 3.31(1+) 96.7 3.41(1+) 66.4 3.51(1+) 99.7

3.15, 3.68 3.15, 4.07

4.97, 7.30

405, 535

AB

70 -221

B,,B,

2.48, 4.41 157, 227 37.9 ,41.4 2211,199o

15.3 (O+) 81.9 15.3 (O+) 88.1

8.15(0+) 89.8

6.34(0+) 81.4 5.83(1+) 82.4

Initial Survival ;,,W, density/m* (%) (age,years)

250

73 132

180

109 185

287 488 483 359 501 1119

472 473 594 327 619 797 613 548

461 205 515

P

17.8 20.9 31.7 65.2 10.2 9.10

31.8 31.7 8.60 31.3 7.70 12.2 7.73 17.7

29.3 27.7 10.6

3.68

250 35.9

3.67

4.00

8.99

FIP

: c0

Amount*** of food 0.39 1.13 0.49 0.58 0.51 0.58 0.57 0.51 0.51 0.00 0.51 0.51 0.19 0.10 0.10 0.20 0.49 0.49 1.02

Type** of food

PP C

PP PP LP LP LP

PP LP LP LP LP

PP PP LP

PP PP PP

Trial Pond No. type*

B B

A B A B B

A A

A A B

A B A

A A A

24 25

26 27 28 29 30

31 32 33A 34 35 36

37 38 39

40 41 42

2

3

5

10

15

Approx. initial density/m2

14.6 (0+) 14.6 (0+) 15.3 (0+)

10.2 (0+) 9.84(0+) 10.2 (o+)

5.11(0+) 5.11(0+) 5.11(0+) 5.11(0+) 5.11(1+) 6.38(0+)

3.65(0+) 3.50(0+) 3.07(1+) 3.49(1+) 3.41(1+)

1.58(1+) 1.82(2+)

71.0 89.5 49.5

82.9 64.4 83.6

85.7 87.1 77.1 75.7 75.7 64.5

76.0 92.9 78.6 74.8 86.2

82.2 30.7

Initial Survival density/m* (%) (age,years)

1.85 2.48 4.94

5.54, 17.6 5.54, 18.7 11.0 ,37.1

0.06, 0.06, 0.06,

11.0 , 36.9 11.0 ,43.0 11.0 , 22.6 22.2 , 60.7 37.8 , 69.3 0.06, 4.96

9.99,42.9 11.0 , 39.9 46.5 , 81.3 61.0 , 88.9 18.7 ) 53.5

52.2 , 81.1 70.4 ,91.8

We,G4

157 157 422 809,1824 809,2443 1686,2816

6.1, 5.9, 6.1,

562,1616 562,1915 562, 891 1134,2348 1931,268l 3.8, 204

365,119O 385,1297 1425,1958 2129,232l 635,157l

824,1052 1281, 513

B,,&

1015 1634 1130

151 151 416

1054 1353 329 1214 750 200

825 912 533 192 936

228 -768

AB

*Pond type: A, concrete, area 14 ma; B, clay, mean area 115 m2. **Food type: LP, lucerne pellets; C, compost (Cl old compost, C? no fertilizer added); PP, poultry laying pellets. ***Amount: total material added to a pond over the 4-month trial period (kg/m*). iir : mean initial individual weight of marron (g). -0 : mean final individual weight (g). : initial biomass (kg/ha). ;; : final biomass (kg/ha). B, AB : change jn biomass, B,-B,. P : production (kg/ha). FIP : amount of food added (kg/ha)/production.

Season

--

411 223

1443 1799 2678

159 172 433

1208 1504 514 1678 1386 222

1017 967 937 838 1089

P

9.50

3.42 2.74 3.82

6.43 5.72 4.53

3.02 3.65 8.56

4.23 3.40 -

4.85 6.03 5.40 6.93 5.19

50.5

PIP

E b