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Polyculture of Nile tilapia (Oreochromis niloticus) and Australian red claw crayfish (Cherax quadricarinatus) in earthen ponds
Aquaculture Aquaculture 122 ( 1994) 47-54
ELSEVIER
Polyculture of Nile tilapia ( Oreochromis niloticus > and Australian red claw crayfish (Cherax quadricarinatus) in earthen ponds Randall
E. BrummettaT*,
Noel C. Alonb
“ICL,ARM/GTZ Africa Aquaculture Project, P.O. Box 229, Zomba, Malawi bBluewaters International, Inc., 4350 East West Highway, Suite 600, Bethesda, MD 20814, USA
(Accepted 28 October 1993)
Abstract
Nile .tilapia (Oreochromis niloticus) and Australian red claw crayfish (Cherax quadriwere cultured alone and together in replicate 0.02 ha earthen ponds to assess the nature and intensity of species interaction in polyculture. Treatments were: (I) 10000 tilapia per hectare, (II) 10000 tilapia plus 25000 crayfish per hectare and (III) 25000 crayfish per hectare. All ponds were fed a 32% crude protein, pelleted catfish feed at monthly-adjusted rates based on stocked tilapia biomass. After 100 days of polyculture, ponds were harvested. Tilapia growth, reproduction and food conversion were adversely affected by the presence of crayfish (PC 0.0 1). Crayfish growth, incidence of intersexuality and percentage of berried females were not affected by the presence of tilapia (PC 0.0 1). carinat;As)
1. Introduction The Nile tilapia (Oreochromis niloticus) is a popular food-fish in many tropical areas, and is hardy and fast-growing under a wide variety of management schemes. The red claw crayfish also grows rapidly and, unlike the Malaysian prawn (Mucrobruchium rosenbergii) which has been polycultured with tilapia and which needs salt water during the larval stages, can easily be spawned and grown entirely in fresh water. A polyculture of the Nile tilapia with the Australian red claw crayfish ( Cherux quadricurinutus) could have several advantages for the tropical freshwater fish farmer. Polyculture of a crustacean with a tintish species has been shown to be a more -*Corresponding author. 0044-8486/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDZOO44-8486(93)E0264-A
48
R.E. Brummett, N. C. Alon /Aquaculture
122 (I 994) 4 7-54
efficient use of pond inputs than monoculture (Malecha et al., 198 1; Rouse and Stickney, 1982 ). Polyculture of tilapia with the Malaysian prawn has shown that species competition was negligible and that yield was increased over either monoculture (Rouse and Stickney, 1982; Behrends et al., 1985 ) . Cohen et al. ( 1983 ) found that the presence of filter-feeding fish (such as the Nile tilapia) improved water quality for prawn production. A successful polyculture of the Nile tilapia with the Australian red claw crayfish would produce low-cost fish flesh for domestic consumption as well as a potentially high-value crustacean cash crop. A common problem with tilapia is their tendency to reproduce at an early age under culture conditions. The benthic red claw crayfish tend to aggregate in large numbers (Jones, 1990; Masser et al., 1991). This behavior, in concert with the simple occupation of space on the substratum, might disrupt the spawning behavior of the tilapia and thereby reduce their reproduction. The objectives of this study were to determine whether species interaction between the Nile tilapia and the red claw crayfish in polyculture would be synergistic or antagonistic in terms of growth rate and total production, and to assess the impact of red claw crayfish on tilapia reproduction in ponds.
2. Materials and methods The 0.02 ha earthen ponds used in this study are located at the University of South Carolina’s aquaculture research facility in McClellanville, South Carolina. The ponds have a sandy-clay bottom and average 1.O m in depth. The well-water used to till the ponds contained 32 mgsl-’ chloride, 41 mgsl-’ calcium and 130 mgsl-’ total hardness. After exposure to atmospheric pressure for 24 h, the pH was 7.46. Following the normal practices of Bluewaters, Inc., a commercial red claw crayfish farm located in Monck’s Corner, South Carolina, 1150 kgeha- ’ of CaCO, was broadcast over each pond bottom prior to filling to insure adequate calcium for ecdysis. Dissolved oxygen was checked each morning with a Yellow Springs model 54 polarographic oxygen meter but, other than adding water as necessary to compensate for losses due to evaporation and seepage, no control over water quality was necessary during grow-out. Prior to stocking, the ponds contained dense growths of Typha, Potamogeton and Ranunculus which covered 30-50% of the pond surface. These were cut at ground-level just before stocking and allowed to regrow. Unpublished data from the previous year indicated that weeds and decaying vegetation in the pond supported, without additional feed inputs, satisfactory red claw crayfish growth rates at the stocking density used in this study. As protection from predators, bird netting was placed around the pond edges, extending one meter over the surface. A 30 cm high solid aluminum strip was erected around the perimeter of the pond site to prevent out-migration of red claw crayfish from the ponds and in-migration of wild crayfish to the ponds. Treatments and replications were assigned using a completely randomized experimental design with three treatments each replicated three times. Stocking rates
R.E. Brummett, N.C. Alon /Aquaculture
122 (1994) 47-54
49
were based on those used by tilapia and red claw crayfish producers (Bluewaters, Inc., in the case of the crayfish) in coastal South Carolina: (I) 10000 0. niloticus per hectare, (II) 10000 0. niloticus plus 25000 C. quadricarinatus per hectare, and (III) 25000 C. quadricarinatus per hectare. Juvenile red claw crayfish (average weight = 3.9 g) were imported from Australia and acclimatized in indoor tanks for 1 week. The juveniles were hand-sorted according to size in order to minimize variation in size at stocking between individuals within ponds. In Malaysian prawns, this variability has been shown to be magnified over the grow-out period, resulting in very high standard errors of means (Sandifer and Smith, 1985 ). The numbers to be stocked into each pond were counteld into pans, weighed and stocked on 29 April 199 1. Fingerlings of the Egypt strain of 0. niloticus, offspring of randomly-spawned broodfsh obtained from Auburn University, were mechanically graded through a 2-cm bar grader which selects individuals greater than 50 g. Individuals weighing 60 g or over were removed by hand. This procedure produced a highly uniform 60% male and 40% female population with an average weight of 53.9 g. This size til.apia was considered small enough to significantly increase their weight, and large enough to spawn at least once during the projected grow-out period. For each pond, fish were weighed in four lots of 50 fish and stocked on 8 July. The delay between stocking of red claw and tilapia was to minimize potential predation of small red claw by tilapia juveniles (Rouse et al., 1987 ) . All ponds received a 32% crude protein, floating catfish pellet once daily between 1: 00 and 2 : 00 p.m. Floating pellets were used in order to minimize competition between tilapia and crayfish for food (Rouse and Stickney, 1982). The hypothesized polyculture was based on the assumption (based on unpublished production records at Bluewaters International, Inc.) that the benthic crayfish would grow well on a diet of decaying vegetation, a food resource which might be less well utilized by the tilapia. Feed rates were based on pooled, monthly 10% samples of stocked tilapia, excluding reproduction. All ponds received the same amount of feed. Feed was added to the crayfish only treatment in order to correct for the: potential fertilizer value of the feed on macrophyte growth. Feed rate per pond increased from 40 kg-ha- ‘day-’ (7.5% bw) initially to 75 kg-ha--‘-day- ’ (2.5% bw). Further increases were not made in order to avoid low dissolved oxygen conditions. Low dissolved oxygen dramatically increases red claw crayfish susceptibility to predation, presumably by forcing them into shallow water to gain access to atmospheric oxygen (Huner and Barr, 1984; Jones, 1990). All ponds were harvested on October 15 after 170 days of red claw and 100 days of tilapia growth. Crayfish and tilapia were separated, sorted by sex, weighed and counted. Female crayfish were further examined for the presence of eggs. Tilapia reproduction from each pond was weighed, but not counted. Average weights and variances were calculated for adult tilapia and crayfish. Food conversio:n ratios were calculated by dividing the total dry weight of food added to the pond by the total wet weight of net tilapia and crayfish biomass. Equality of variances was verified with the variance ratio test, and means were compared
50
R.E. Brummett, N.C. Alon /Aquaculture 122 (1994) 47-54
using Student’s t-test (Zar, 1974). To correct for differences in initial crayfish stocking weight we compared specific growth rates of Hepher ( 1980): SGR=
(3wP.33
-
wZ.33)
t-t,
3. Results Survival of red claw crayfish averaged 40.1% (Table 1) . Predation by alligators, egrets, frogs, herons, raccoons and snakes was verified by visual observation and predator stomach examination and appeared to account for most losses. No wild crayfish were found in any ponds. Variance in average final tilapia and crayfish weight within treatments was generally low (Table 1). However, in replication three in treatment III (25000 crayfish-ha- ’ ) both survival and average weight were approximately l/2 that in the other two replications. Such an observation might be the result of a chronic water quality or disease problem in this pond, but we have no direct evidence of either having occurred. Red claw crayfish specific growth (Hepher, 1988 ) averaged 0.040 g-day- ‘. No Table 1 Stocking rates, initial and final average weights and survivals from an assessment of interaction between Nile tilapia (0. niloticus) and Australian red claw crayfish (C. quadricarinatus) in polyculture Stocking rate (no:ha-I)
10 000 Tilapia
Replicate
1
?
L
3 AVG s.d. 10 000 Tilapia 25 000 Red claw
1 2 3 AVG s.d.
25 000 Red claw
1 2 3 AVG s.d.
Initial weight (g)”
Final weight (g )
Survival (% )
Tilapia
Tilapia
Tilapia
Crayfish
54.0 54.0 54.0 54.0
53.5 54.0 53.5 53.7 0.02
Crayfish
76.5 88.5 88.5 84.5 10.7
_ -
49.9 54.0 57.1 53.7 2.9
92.5 16.5 95.5 88.2 23.2
41.2 46.6 45.6 44.5 1.8
67.4 63.7 31.1 56.1 60.7
-
42.8 44.0 20.6 35.8 38.6
217.8 197.0 206.9 201.2 24.1 4.9 4.1 5.1 4.9 0.009 2.0 2.1 2.0 2.0 0.002
183.5 186.8 184.2 184.8 0.7
Crayfish
‘Tilapia were graded to produce a highly uniform population for stocking. Crayfish were hand-sorted to minimize within-pond variability.
R.E. Brummett, N.C. Alon /Aquaculture
122 (1994) 47-54
51
significant difference (PC 0.0 1) in final average weight between monoculture and polyculture was noted (Table 2). Likewise, frequencies of intersexual and berried female crayfish were not affected by the presence of tilapia at these stocking densities. Tilalpia average weight was reduced in the presence of crayfish (PC 0.01 ), despite the fact that total standing stock (crayfish biomass plus total tilapia biomass) was significantly higher (P~0.01) when tilapia were grown alone (3386.7 kg. ha-- ’ ) than when polycultured with crayfish (28 11.3 kg-ha- ’ ) . Weight of tilapia reproduction was less in polyculture than in monoculture (PC 0.0 1). Standing stock at harvest of crayfish grown in monoculture was 50 1.2 kg-ha-’ (Table 3). Table 2 Stocking rate, final weight, specific growth rate (SGR) and frequency of intersexuality and berried females (as a percentage of all females) in Australian red claw crayfish (C. quadricarinatus) grown alone and in polyculture with Nile tilapia (0. niloticus) Stocking rate (no:ha-r)
Replicate
25 000 red claw
1 2 3 AVG s.d. 1 2 3 AVG s.d.
25 000 Red claw 10 000 Tilapia
3 ( pyJ.33 *SGR= --t-_~--
-
Final weight (g)
SGR* (g-day-’
Males
Females
Intersex
78.8 75.9 39.3 64.7” 17.98 55.1 60.1 68.0 61.3” 5.09
56.6 54.1 34.9 48.5b 9.69 44.5 47.4 48.0 46.6b 1.53
66.5 51.2 38.0 51.9b 11.65 48.7 52.3 55.5 52.2b 2.78
)
0.049 0.047 0.036 0.044” 0.0057 0.034 0.036 0.037 0.036” 0.0012
Females berried (%) 4.67 2.27 1.94 2.96a 1.217 4.37 1.72 1.75 2.61” 1.242
26.9 33.9 5.9 22.2” 11.90 36.4 41.1 30.9 36.1” 4.17
pfl~33)
(Hepher, 1988). 0 Values with different associated letters are significantly different (PC 0.01).
Table 3 Stockin,g rate, final tilapia average weight, total (all tilapia plus crayfish) standing stock, weight of tilapia reproduction and total food conversion ratio (FCR) for monocultures and a polyculture of Nile tilapia (0. niloticus) and Australian red claw crayfish (C. quadricarinatus) Stocking rate (no:ha-‘)
Tilapia average weight (g)
Total standing stock (kg-ha-‘)
Tilapia reproduction (kg-ha-‘)
FCR
10 000 IO 000 25 000 25 000
207.3” 184.9b
3386.7a 281 1.3b
1639.5a 585.0b
1.38” 1.82b
-
501.2’
Tilapia Tilapia Red claw !Red claw
Values in columns with different letters are significantly different (PC 0.0 1).
8.67’
52
R.E. Brummett, NC. Alon /Aquaculture 122 (1994) 47-54
The food conversion ratio (FCR, calculated as total dry weight of feed added divided by total increase from stocking in wet tilapia plus crayfish biomass) was significantly better (PC 0.0 1) for tilapia monoculture (FCR = 1.38 ) than for polyculture (FCR= 1.82). FCR for crayfish monoculture was 8.67 (Table 3 ).
4. Discussion Average survival of red claw crayfish in this study (40.1%) was within the range of reported results. Survival in grow-out studies normally ranges from 30 to SO%, depending upon stocking size and density, water quality, and other environmental factors (Sammy, 1988; Jones, 1988; Medley, 199 1; Rouse et al., 199 1). Unpublished survival figures from previous years at the University of South Carolina ranged from 20 to 45%. Average crayfish absolute growth in this study (0.040 g-day- ’ ) was within the 0.034-0.046 g-day-’ range of values reported for red claw crayfish monocultures receiving supplemental feeds (Jones, 1988; Medley, 199 1). Unpublished absolute growth coefficients from previous and subsequent research conducted at the University of South Carolina on red claw crayfish monocultures fed exclusively on natural vegetation were in the range of 0.040-0.054 g-day-‘. The low values in replicate three of treatment III affect the statistical analysis. If the trend indicated by replicates one and two is real and the low values in replicate three are merely an artifact, then the argument could be made that red claw crayfish grow better in monoculture than in polyculture with tilapia. However, there is no evidence to support the exclusion of replicate three. The frequencies of egg-bearing females and intersexual individuals within the crayfish population were the same under monoculture as under polyculture with tilapia. Occurrence of intersexes among Australian parastacid crayfish is fairly common, with several species known to possess external sexual characters in different combinations (Sokol, 1988 ). Whether these intersex individuals are truly functional hermaphrodites or in a transitional sexual phase is not certain (Sokol, 1988; Medley, 199 1). Other cases of “pseudohermaphroditism”, i.e. females with male secondary sex characteristics, is also found in cambarids (Huner and Barr, 198 1). The importance of this trait in commercial and experimental aquaculture lies in the uncertainty it imparts to the prediction of overall population growth rates from combined sex-specific rates. The presence of Australian red claw crayfish seems to disrupt tilapia feeding and spawning behavior as indicated by the significantly lower tilapia growth and reproduction in polyculture versus monoculture. Both red claw crayfish and tilapia feed on microbially-enriched detritus (Schroeder, 1980; Cange et al., 1983; Huner and Barr, 1984; Jones, 1988) and may be competing for this food supply in polyculture. However, only tilapia growth was adversely affected by this competition. Red claw crayfish either out-competed the tilapia or found sufficient food in the natural vegetation. On the other hand, tilapia, which rely on natural pond food organisms for 60-80% of their growth even in fed ponds (Schroeder,
R.E. Brummett, N.C. Alon /Aquaculture 122 (1994) 47-54
53
1983)) seem to have been impeded in their access to the substratum with its potential food resources. This hypothesis is supported by the reduced spawning success in the ponds containing crayfish. Even in the absence of antagonistic interspecific interaction, the physical presence of crayfish seems to have sufficiently limited access to the substratum to result in the observed decrease in average tilapia growth, food conversion efficiency and reproduction in polyculture. If an extra expenditure of energy for tilapia nest-building and territorial defense was necessitated by the presence of the crayfish, male tilapia, which build and de:fend the nests, might be expected to suffer disproportionately. In this study, male tilapia average weight was reduced by 12.27% in the presence of crayfish whereas female tilapia weight was reduced by only 5.71%. Alternatively, disruption of tilapia feeding activity by crayfish may have reduced growth similarly in both tilapia sexes. The simultaneous interference with spawning activity may have then reduced the brooding load on the female tilapia, permitting them to eat and grow more than would have otherwise been the case. It might be possible to test this hypothesis by comparing growth rates of male and female tilapia co-stocked in ponds with red claw crayfish, and those of tilapia stocked in cages with a sufficiently large mesh size to prohibit the collection and incubation of eggs (Pagan-Font, 1975; Meriwether et al., 1984). The polyculture of Nile tilapia and Australian red claw crayfish is feasible under the circumstances tested here if the crayfish is the species of primary interest, or if specific circumstances render the observed reduction in tilapia growth rate econo:mically insignificant. However, if tilapia growth and standing stock are to be maximized, monoculture of tilapia should be considered. Alternatively, some lower density of red claw crayfish than that used in this study might allow tilapia growth to be maximized and tilapia reproduction minimized.
5. References Behrends, L.L., Kingsley, J.B. and Price III, A.H., 1985. Polyculture of freshwater prawns, tilapia, channel cattish and Chinese carps. J. World Maricult. Sot., 16: 436-450. Cange, SW., Avault, J.W. Jr., Perry, W.G. and Tarver, J., 1983. A note on the potential and constraints for culture of Macrobrachium rosenbergii in the southeastern United States. In: G.L. Rogers, R. Day and A. Lim (Editors), Proceedings of the First International Conference on Warmwater Aquaculture - Crustacea. Brigham Young Hawaii Campus, Office of Continuing Education, Laie, HI, pp. 46-49. Cohen, D., Ra’anan, Z. and Barnes, A., 1983. The production of freshwater prawn Macrobrachium rose.qbergiiin Israel. Aquaculture, 3 1: 67-76. Hepher, B., 1988. Nutrition of Pond Fishes. Cambridge University Press, Cambridge, UK, 388 pp. Huner, J. and Barr, J.E., 198 1. Red Swamp Crayfish: Biology and Exploitation. Sea Grant Publication. LSU-T-80-001. Louisiana Sea Grant. Louisiana State University. Baton Rouge, LA. Jones, CM., 1988. Aquaculture potential of Cherax quadricarinatus: research objectives and preliminary results. In: L.H. Evans and D. O’Sullivan (Editors), Proceedings of the First Australian Shellfish Aquaculture Conference, Curtin University of Technology, Western Australia, pp. 7378. Jones, CM., 1990. The biology and aquaculture potential of the tropical freshwater crayfish, Cherax
54
R.E. Brummett. N.C. Alon / Aquaculture 122 (1994) 47-54
quadricarinatus. Queensland Department of Primary Industries, Fisheries Branch Research Station, Walkamin, Qld., 4872, 13 1 pp. Malecha, S., Buck, D.H., Baur, R.J. and Onizuka, D.R., 198 1. Polyculture of the freshwater prawn, Macrobrachium rosenbergii, Chinese and common carps in ponds enriched with swine manure. I. initial trials. Aquaculture, 25: 101-l 16. Masser, M., Rouse, D. and Austin, C., 199 1. Australian Red Claw Crayfish: A Potential Culture Species for Alabama. Alabama Cooperative Extension Service. Auburn University, Auburn, AL. Medley, P.B., 199 1. Suitability of the Australian red claw, Cherax quadricarinatus (von Martens) for aquaculture in the southeastern United States. MS Thesis, Auburn University, Auburn, AL (unpbl. ), 102 pp. Meriwether, F.H., Scura, E.D., and Okamura, W.Y., 1984. Cage culture of red tilapia in prawn and shrimp ponds. J. World Maricult. Sot., 15: 254-265. Pagan-Font, F.A.. 1975. Cage culture as a mechanical method for controlling reproduction of Tilapia aurea. Aquaculture, 6: 243-247. Rouse, D.B. and Stickney, R.R., 1982. Evaluation of the production potential of Macrobrachium rosenbergii in monoculture and in polyculture with Tilapia aurea. J. World Maricult. Sot., 13: 7385. Rouse, D.B., El Naggar, G.O. and Mulla, M.A., 1987. Effects of stocking size and density of tilapia on Macrobrachium rosenbergii in polyculture. J. World Aquacult. Sot., 18: 57-60. Rouse, D.B., Austin, C.M. and Medley, P.B., 199 1. Progress toward profits? Information on the Australian crayfish. Aquacult. Mag., 17 (3): 46-56. Sammy, N., 1988. Breeding biology of Cherax quadricarinatus in the Northern Territory. In: L.H. Evans and D. O’Sullivan (Editors), Proceedings of the First Australian Shellfish Aquaculture Conference, Curtin University of Technology, Western Australia, pp. 79-88. Sandifer, P.A. and Smith, T.I.J., 1985. Freshwater prawns. In: J.V. Huner and E.E. Brown (Editors), Crustacean and Mollusk Aquaculture in the United States. AVI Publishing, Westport, CN, pp. 63125. Schroeder, G.L., 1980. Fish farming in manure-loaded ponds. In: R.S.V. Pullin and Z.H. Shehadeh (Editors), Integrated Agriculture-Aquaculture Farming Systems. ICLARM Conference Proceedings 4. International Center for Living Aquatic Resources Management, Manila, Philippines and the Southeast Asian Center for Graduate Study and Research in Agriculture College, Los Banos, Laguna, Philippines, pp. 73-86. Schroeder, G.L., 1983. Sources of fish and prawn growth in polyculture ponds as indicated by d C analysis. Aquaculture, 35: 29-42. Sokol, A., 1988. The Australian yabby. In: D.M. Holdrich and R.S. Lowery (Editors), Freshwater Crayfish: Biology, Management and Exploitation. Timber Press, Portland, OR, pp. 401-425. Zar. J.H. 1974. Biostatistical Analysis. Prentice Hall, Englewood Cliffs, NJ, 620 pp.
ELSEVIER
Polyculture of Nile tilapia ( Oreochromis niloticus > and Australian red claw crayfish (Cherax quadricarinatus) in earthen ponds Randall
E. BrummettaT*,
Noel C. Alonb
“ICL,ARM/GTZ Africa Aquaculture Project, P.O. Box 229, Zomba, Malawi bBluewaters International, Inc., 4350 East West Highway, Suite 600, Bethesda, MD 20814, USA
(Accepted 28 October 1993)
Abstract
Nile .tilapia (Oreochromis niloticus) and Australian red claw crayfish (Cherax quadriwere cultured alone and together in replicate 0.02 ha earthen ponds to assess the nature and intensity of species interaction in polyculture. Treatments were: (I) 10000 tilapia per hectare, (II) 10000 tilapia plus 25000 crayfish per hectare and (III) 25000 crayfish per hectare. All ponds were fed a 32% crude protein, pelleted catfish feed at monthly-adjusted rates based on stocked tilapia biomass. After 100 days of polyculture, ponds were harvested. Tilapia growth, reproduction and food conversion were adversely affected by the presence of crayfish (PC 0.0 1). Crayfish growth, incidence of intersexuality and percentage of berried females were not affected by the presence of tilapia (PC 0.0 1). carinat;As)
1. Introduction The Nile tilapia (Oreochromis niloticus) is a popular food-fish in many tropical areas, and is hardy and fast-growing under a wide variety of management schemes. The red claw crayfish also grows rapidly and, unlike the Malaysian prawn (Mucrobruchium rosenbergii) which has been polycultured with tilapia and which needs salt water during the larval stages, can easily be spawned and grown entirely in fresh water. A polyculture of the Nile tilapia with the Australian red claw crayfish ( Cherux quadricurinutus) could have several advantages for the tropical freshwater fish farmer. Polyculture of a crustacean with a tintish species has been shown to be a more -*Corresponding author. 0044-8486/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDZOO44-8486(93)E0264-A
48
R.E. Brummett, N. C. Alon /Aquaculture
122 (I 994) 4 7-54
efficient use of pond inputs than monoculture (Malecha et al., 198 1; Rouse and Stickney, 1982 ). Polyculture of tilapia with the Malaysian prawn has shown that species competition was negligible and that yield was increased over either monoculture (Rouse and Stickney, 1982; Behrends et al., 1985 ) . Cohen et al. ( 1983 ) found that the presence of filter-feeding fish (such as the Nile tilapia) improved water quality for prawn production. A successful polyculture of the Nile tilapia with the Australian red claw crayfish would produce low-cost fish flesh for domestic consumption as well as a potentially high-value crustacean cash crop. A common problem with tilapia is their tendency to reproduce at an early age under culture conditions. The benthic red claw crayfish tend to aggregate in large numbers (Jones, 1990; Masser et al., 1991). This behavior, in concert with the simple occupation of space on the substratum, might disrupt the spawning behavior of the tilapia and thereby reduce their reproduction. The objectives of this study were to determine whether species interaction between the Nile tilapia and the red claw crayfish in polyculture would be synergistic or antagonistic in terms of growth rate and total production, and to assess the impact of red claw crayfish on tilapia reproduction in ponds.
2. Materials and methods The 0.02 ha earthen ponds used in this study are located at the University of South Carolina’s aquaculture research facility in McClellanville, South Carolina. The ponds have a sandy-clay bottom and average 1.O m in depth. The well-water used to till the ponds contained 32 mgsl-’ chloride, 41 mgsl-’ calcium and 130 mgsl-’ total hardness. After exposure to atmospheric pressure for 24 h, the pH was 7.46. Following the normal practices of Bluewaters, Inc., a commercial red claw crayfish farm located in Monck’s Corner, South Carolina, 1150 kgeha- ’ of CaCO, was broadcast over each pond bottom prior to filling to insure adequate calcium for ecdysis. Dissolved oxygen was checked each morning with a Yellow Springs model 54 polarographic oxygen meter but, other than adding water as necessary to compensate for losses due to evaporation and seepage, no control over water quality was necessary during grow-out. Prior to stocking, the ponds contained dense growths of Typha, Potamogeton and Ranunculus which covered 30-50% of the pond surface. These were cut at ground-level just before stocking and allowed to regrow. Unpublished data from the previous year indicated that weeds and decaying vegetation in the pond supported, without additional feed inputs, satisfactory red claw crayfish growth rates at the stocking density used in this study. As protection from predators, bird netting was placed around the pond edges, extending one meter over the surface. A 30 cm high solid aluminum strip was erected around the perimeter of the pond site to prevent out-migration of red claw crayfish from the ponds and in-migration of wild crayfish to the ponds. Treatments and replications were assigned using a completely randomized experimental design with three treatments each replicated three times. Stocking rates
R.E. Brummett, N.C. Alon /Aquaculture
122 (1994) 47-54
49
were based on those used by tilapia and red claw crayfish producers (Bluewaters, Inc., in the case of the crayfish) in coastal South Carolina: (I) 10000 0. niloticus per hectare, (II) 10000 0. niloticus plus 25000 C. quadricarinatus per hectare, and (III) 25000 C. quadricarinatus per hectare. Juvenile red claw crayfish (average weight = 3.9 g) were imported from Australia and acclimatized in indoor tanks for 1 week. The juveniles were hand-sorted according to size in order to minimize variation in size at stocking between individuals within ponds. In Malaysian prawns, this variability has been shown to be magnified over the grow-out period, resulting in very high standard errors of means (Sandifer and Smith, 1985 ). The numbers to be stocked into each pond were counteld into pans, weighed and stocked on 29 April 199 1. Fingerlings of the Egypt strain of 0. niloticus, offspring of randomly-spawned broodfsh obtained from Auburn University, were mechanically graded through a 2-cm bar grader which selects individuals greater than 50 g. Individuals weighing 60 g or over were removed by hand. This procedure produced a highly uniform 60% male and 40% female population with an average weight of 53.9 g. This size til.apia was considered small enough to significantly increase their weight, and large enough to spawn at least once during the projected grow-out period. For each pond, fish were weighed in four lots of 50 fish and stocked on 8 July. The delay between stocking of red claw and tilapia was to minimize potential predation of small red claw by tilapia juveniles (Rouse et al., 1987 ) . All ponds received a 32% crude protein, floating catfish pellet once daily between 1: 00 and 2 : 00 p.m. Floating pellets were used in order to minimize competition between tilapia and crayfish for food (Rouse and Stickney, 1982). The hypothesized polyculture was based on the assumption (based on unpublished production records at Bluewaters International, Inc.) that the benthic crayfish would grow well on a diet of decaying vegetation, a food resource which might be less well utilized by the tilapia. Feed rates were based on pooled, monthly 10% samples of stocked tilapia, excluding reproduction. All ponds received the same amount of feed. Feed was added to the crayfish only treatment in order to correct for the: potential fertilizer value of the feed on macrophyte growth. Feed rate per pond increased from 40 kg-ha- ‘day-’ (7.5% bw) initially to 75 kg-ha--‘-day- ’ (2.5% bw). Further increases were not made in order to avoid low dissolved oxygen conditions. Low dissolved oxygen dramatically increases red claw crayfish susceptibility to predation, presumably by forcing them into shallow water to gain access to atmospheric oxygen (Huner and Barr, 1984; Jones, 1990). All ponds were harvested on October 15 after 170 days of red claw and 100 days of tilapia growth. Crayfish and tilapia were separated, sorted by sex, weighed and counted. Female crayfish were further examined for the presence of eggs. Tilapia reproduction from each pond was weighed, but not counted. Average weights and variances were calculated for adult tilapia and crayfish. Food conversio:n ratios were calculated by dividing the total dry weight of food added to the pond by the total wet weight of net tilapia and crayfish biomass. Equality of variances was verified with the variance ratio test, and means were compared
50
R.E. Brummett, N.C. Alon /Aquaculture 122 (1994) 47-54
using Student’s t-test (Zar, 1974). To correct for differences in initial crayfish stocking weight we compared specific growth rates of Hepher ( 1980): SGR=
(3wP.33
-
wZ.33)
t-t,
3. Results Survival of red claw crayfish averaged 40.1% (Table 1) . Predation by alligators, egrets, frogs, herons, raccoons and snakes was verified by visual observation and predator stomach examination and appeared to account for most losses. No wild crayfish were found in any ponds. Variance in average final tilapia and crayfish weight within treatments was generally low (Table 1). However, in replication three in treatment III (25000 crayfish-ha- ’ ) both survival and average weight were approximately l/2 that in the other two replications. Such an observation might be the result of a chronic water quality or disease problem in this pond, but we have no direct evidence of either having occurred. Red claw crayfish specific growth (Hepher, 1988 ) averaged 0.040 g-day- ‘. No Table 1 Stocking rates, initial and final average weights and survivals from an assessment of interaction between Nile tilapia (0. niloticus) and Australian red claw crayfish (C. quadricarinatus) in polyculture Stocking rate (no:ha-I)
10 000 Tilapia
Replicate
1
?
L
3 AVG s.d. 10 000 Tilapia 25 000 Red claw
1 2 3 AVG s.d.
25 000 Red claw
1 2 3 AVG s.d.
Initial weight (g)”
Final weight (g )
Survival (% )
Tilapia
Tilapia
Tilapia
Crayfish
54.0 54.0 54.0 54.0
53.5 54.0 53.5 53.7 0.02
Crayfish
76.5 88.5 88.5 84.5 10.7
_ -
49.9 54.0 57.1 53.7 2.9
92.5 16.5 95.5 88.2 23.2
41.2 46.6 45.6 44.5 1.8
67.4 63.7 31.1 56.1 60.7
-
42.8 44.0 20.6 35.8 38.6
217.8 197.0 206.9 201.2 24.1 4.9 4.1 5.1 4.9 0.009 2.0 2.1 2.0 2.0 0.002
183.5 186.8 184.2 184.8 0.7
Crayfish
‘Tilapia were graded to produce a highly uniform population for stocking. Crayfish were hand-sorted to minimize within-pond variability.
R.E. Brummett, N.C. Alon /Aquaculture
122 (1994) 47-54
51
significant difference (PC 0.0 1) in final average weight between monoculture and polyculture was noted (Table 2). Likewise, frequencies of intersexual and berried female crayfish were not affected by the presence of tilapia at these stocking densities. Tilalpia average weight was reduced in the presence of crayfish (PC 0.01 ), despite the fact that total standing stock (crayfish biomass plus total tilapia biomass) was significantly higher (P~0.01) when tilapia were grown alone (3386.7 kg. ha-- ’ ) than when polycultured with crayfish (28 11.3 kg-ha- ’ ) . Weight of tilapia reproduction was less in polyculture than in monoculture (PC 0.0 1). Standing stock at harvest of crayfish grown in monoculture was 50 1.2 kg-ha-’ (Table 3). Table 2 Stocking rate, final weight, specific growth rate (SGR) and frequency of intersexuality and berried females (as a percentage of all females) in Australian red claw crayfish (C. quadricarinatus) grown alone and in polyculture with Nile tilapia (0. niloticus) Stocking rate (no:ha-r)
Replicate
25 000 red claw
1 2 3 AVG s.d. 1 2 3 AVG s.d.
25 000 Red claw 10 000 Tilapia
3 ( pyJ.33 *SGR= --t-_~--
-
Final weight (g)
SGR* (g-day-’
Males
Females
Intersex
78.8 75.9 39.3 64.7” 17.98 55.1 60.1 68.0 61.3” 5.09
56.6 54.1 34.9 48.5b 9.69 44.5 47.4 48.0 46.6b 1.53
66.5 51.2 38.0 51.9b 11.65 48.7 52.3 55.5 52.2b 2.78
)
0.049 0.047 0.036 0.044” 0.0057 0.034 0.036 0.037 0.036” 0.0012
Females berried (%) 4.67 2.27 1.94 2.96a 1.217 4.37 1.72 1.75 2.61” 1.242
26.9 33.9 5.9 22.2” 11.90 36.4 41.1 30.9 36.1” 4.17
pfl~33)
(Hepher, 1988). 0 Values with different associated letters are significantly different (PC 0.01).
Table 3 Stockin,g rate, final tilapia average weight, total (all tilapia plus crayfish) standing stock, weight of tilapia reproduction and total food conversion ratio (FCR) for monocultures and a polyculture of Nile tilapia (0. niloticus) and Australian red claw crayfish (C. quadricarinatus) Stocking rate (no:ha-‘)
Tilapia average weight (g)
Total standing stock (kg-ha-‘)
Tilapia reproduction (kg-ha-‘)
FCR
10 000 IO 000 25 000 25 000
207.3” 184.9b
3386.7a 281 1.3b
1639.5a 585.0b
1.38” 1.82b
-
501.2’
Tilapia Tilapia Red claw !Red claw
Values in columns with different letters are significantly different (PC 0.0 1).
8.67’
52
R.E. Brummett, NC. Alon /Aquaculture 122 (1994) 47-54
The food conversion ratio (FCR, calculated as total dry weight of feed added divided by total increase from stocking in wet tilapia plus crayfish biomass) was significantly better (PC 0.0 1) for tilapia monoculture (FCR = 1.38 ) than for polyculture (FCR= 1.82). FCR for crayfish monoculture was 8.67 (Table 3 ).
4. Discussion Average survival of red claw crayfish in this study (40.1%) was within the range of reported results. Survival in grow-out studies normally ranges from 30 to SO%, depending upon stocking size and density, water quality, and other environmental factors (Sammy, 1988; Jones, 1988; Medley, 199 1; Rouse et al., 199 1). Unpublished survival figures from previous years at the University of South Carolina ranged from 20 to 45%. Average crayfish absolute growth in this study (0.040 g-day- ’ ) was within the 0.034-0.046 g-day-’ range of values reported for red claw crayfish monocultures receiving supplemental feeds (Jones, 1988; Medley, 199 1). Unpublished absolute growth coefficients from previous and subsequent research conducted at the University of South Carolina on red claw crayfish monocultures fed exclusively on natural vegetation were in the range of 0.040-0.054 g-day-‘. The low values in replicate three of treatment III affect the statistical analysis. If the trend indicated by replicates one and two is real and the low values in replicate three are merely an artifact, then the argument could be made that red claw crayfish grow better in monoculture than in polyculture with tilapia. However, there is no evidence to support the exclusion of replicate three. The frequencies of egg-bearing females and intersexual individuals within the crayfish population were the same under monoculture as under polyculture with tilapia. Occurrence of intersexes among Australian parastacid crayfish is fairly common, with several species known to possess external sexual characters in different combinations (Sokol, 1988 ). Whether these intersex individuals are truly functional hermaphrodites or in a transitional sexual phase is not certain (Sokol, 1988; Medley, 199 1). Other cases of “pseudohermaphroditism”, i.e. females with male secondary sex characteristics, is also found in cambarids (Huner and Barr, 198 1). The importance of this trait in commercial and experimental aquaculture lies in the uncertainty it imparts to the prediction of overall population growth rates from combined sex-specific rates. The presence of Australian red claw crayfish seems to disrupt tilapia feeding and spawning behavior as indicated by the significantly lower tilapia growth and reproduction in polyculture versus monoculture. Both red claw crayfish and tilapia feed on microbially-enriched detritus (Schroeder, 1980; Cange et al., 1983; Huner and Barr, 1984; Jones, 1988) and may be competing for this food supply in polyculture. However, only tilapia growth was adversely affected by this competition. Red claw crayfish either out-competed the tilapia or found sufficient food in the natural vegetation. On the other hand, tilapia, which rely on natural pond food organisms for 60-80% of their growth even in fed ponds (Schroeder,
R.E. Brummett, N.C. Alon /Aquaculture 122 (1994) 47-54
53
1983)) seem to have been impeded in their access to the substratum with its potential food resources. This hypothesis is supported by the reduced spawning success in the ponds containing crayfish. Even in the absence of antagonistic interspecific interaction, the physical presence of crayfish seems to have sufficiently limited access to the substratum to result in the observed decrease in average tilapia growth, food conversion efficiency and reproduction in polyculture. If an extra expenditure of energy for tilapia nest-building and territorial defense was necessitated by the presence of the crayfish, male tilapia, which build and de:fend the nests, might be expected to suffer disproportionately. In this study, male tilapia average weight was reduced by 12.27% in the presence of crayfish whereas female tilapia weight was reduced by only 5.71%. Alternatively, disruption of tilapia feeding activity by crayfish may have reduced growth similarly in both tilapia sexes. The simultaneous interference with spawning activity may have then reduced the brooding load on the female tilapia, permitting them to eat and grow more than would have otherwise been the case. It might be possible to test this hypothesis by comparing growth rates of male and female tilapia co-stocked in ponds with red claw crayfish, and those of tilapia stocked in cages with a sufficiently large mesh size to prohibit the collection and incubation of eggs (Pagan-Font, 1975; Meriwether et al., 1984). The polyculture of Nile tilapia and Australian red claw crayfish is feasible under the circumstances tested here if the crayfish is the species of primary interest, or if specific circumstances render the observed reduction in tilapia growth rate econo:mically insignificant. However, if tilapia growth and standing stock are to be maximized, monoculture of tilapia should be considered. Alternatively, some lower density of red claw crayfish than that used in this study might allow tilapia growth to be maximized and tilapia reproduction minimized.
5. References Behrends, L.L., Kingsley, J.B. and Price III, A.H., 1985. Polyculture of freshwater prawns, tilapia, channel cattish and Chinese carps. J. World Maricult. Sot., 16: 436-450. Cange, SW., Avault, J.W. Jr., Perry, W.G. and Tarver, J., 1983. A note on the potential and constraints for culture of Macrobrachium rosenbergii in the southeastern United States. In: G.L. Rogers, R. Day and A. Lim (Editors), Proceedings of the First International Conference on Warmwater Aquaculture - Crustacea. Brigham Young Hawaii Campus, Office of Continuing Education, Laie, HI, pp. 46-49. Cohen, D., Ra’anan, Z. and Barnes, A., 1983. The production of freshwater prawn Macrobrachium rose.qbergiiin Israel. Aquaculture, 3 1: 67-76. Hepher, B., 1988. Nutrition of Pond Fishes. Cambridge University Press, Cambridge, UK, 388 pp. Huner, J. and Barr, J.E., 198 1. Red Swamp Crayfish: Biology and Exploitation. Sea Grant Publication. LSU-T-80-001. Louisiana Sea Grant. Louisiana State University. Baton Rouge, LA. Jones, CM., 1988. Aquaculture potential of Cherax quadricarinatus: research objectives and preliminary results. In: L.H. Evans and D. O’Sullivan (Editors), Proceedings of the First Australian Shellfish Aquaculture Conference, Curtin University of Technology, Western Australia, pp. 7378. Jones, CM., 1990. The biology and aquaculture potential of the tropical freshwater crayfish, Cherax
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quadricarinatus. Queensland Department of Primary Industries, Fisheries Branch Research Station, Walkamin, Qld., 4872, 13 1 pp. Malecha, S., Buck, D.H., Baur, R.J. and Onizuka, D.R., 198 1. Polyculture of the freshwater prawn, Macrobrachium rosenbergii, Chinese and common carps in ponds enriched with swine manure. I. initial trials. Aquaculture, 25: 101-l 16. Masser, M., Rouse, D. and Austin, C., 199 1. Australian Red Claw Crayfish: A Potential Culture Species for Alabama. Alabama Cooperative Extension Service. Auburn University, Auburn, AL. Medley, P.B., 199 1. Suitability of the Australian red claw, Cherax quadricarinatus (von Martens) for aquaculture in the southeastern United States. MS Thesis, Auburn University, Auburn, AL (unpbl. ), 102 pp. Meriwether, F.H., Scura, E.D., and Okamura, W.Y., 1984. Cage culture of red tilapia in prawn and shrimp ponds. J. World Maricult. Sot., 15: 254-265. Pagan-Font, F.A.. 1975. Cage culture as a mechanical method for controlling reproduction of Tilapia aurea. Aquaculture, 6: 243-247. Rouse, D.B. and Stickney, R.R., 1982. Evaluation of the production potential of Macrobrachium rosenbergii in monoculture and in polyculture with Tilapia aurea. J. World Maricult. Sot., 13: 7385. Rouse, D.B., El Naggar, G.O. and Mulla, M.A., 1987. Effects of stocking size and density of tilapia on Macrobrachium rosenbergii in polyculture. J. World Aquacult. Sot., 18: 57-60. Rouse, D.B., Austin, C.M. and Medley, P.B., 199 1. Progress toward profits? Information on the Australian crayfish. Aquacult. Mag., 17 (3): 46-56. Sammy, N., 1988. Breeding biology of Cherax quadricarinatus in the Northern Territory. In: L.H. Evans and D. O’Sullivan (Editors), Proceedings of the First Australian Shellfish Aquaculture Conference, Curtin University of Technology, Western Australia, pp. 79-88. Sandifer, P.A. and Smith, T.I.J., 1985. Freshwater prawns. In: J.V. Huner and E.E. Brown (Editors), Crustacean and Mollusk Aquaculture in the United States. AVI Publishing, Westport, CN, pp. 63125. Schroeder, G.L., 1980. Fish farming in manure-loaded ponds. In: R.S.V. Pullin and Z.H. Shehadeh (Editors), Integrated Agriculture-Aquaculture Farming Systems. ICLARM Conference Proceedings 4. International Center for Living Aquatic Resources Management, Manila, Philippines and the Southeast Asian Center for Graduate Study and Research in Agriculture College, Los Banos, Laguna, Philippines, pp. 73-86. Schroeder, G.L., 1983. Sources of fish and prawn growth in polyculture ponds as indicated by d C analysis. Aquaculture, 35: 29-42. Sokol, A., 1988. The Australian yabby. In: D.M. Holdrich and R.S. Lowery (Editors), Freshwater Crayfish: Biology, Management and Exploitation. Timber Press, Portland, OR, pp. 401-425. Zar. J.H. 1974. Biostatistical Analysis. Prentice Hall, Englewood Cliffs, NJ, 620 pp.