The Intensive Culture of the Penaeid Shrimp Penaeus vannamei Boone in a Recirculating Raceway System

Recirculating raceway systems were examined for their potential as a method for the intensive culture of the marine shrimp Penaeus vannamei Boone. The systems consisted of fiberglass raceways 38 m³ (13.7 m ± 2.4 m ± 1.16 m) and 28 m³ (13.7 m ± 2.4 m ± 0.85 m) each equipped with a vertical screen biofilter, foam fractionators and an ultraviolet ozone generator. All of the systems were enclosed in a commercial greenhouse. Four preliminary growout experiments and two growout experiments with stocking densities of 970 shrimp/m³ and 2,132 shrimp/m³ were completed.
Temperature, pH and salinity remained constant throughout the experiments. Unionized ammonia levels remained below 0.2 mg/L. Nitrite levels ranged from 0.1 to 1.0 mg/L. The 2,132/m² stocking density resulted in 48% survival, food conversion ratio (FCR) of 1.8 and an average size of 10.8 g. The 970/m³ stocking density resulted in 82% survival, FCR of 2, and an average size of 14 g. Production was 11.4 kg/m³ (114 tons/ha) and 11.0 kg/m³ (110 tons/ha) for the high and low stocking densities, respectively.     

Effects of Stocking Density and Monosex Culture of Freshwater Prawn Macrobrachium rosenbergii on Growth and Production in Concrete Tanks in Saudi Arabia

Abstract This study was conducted to evaluate the effects of stocking density and monosex culture on growth, survival, yield and feed conversion ratio of freshwater prawn Macrobrachium rosenbergii in concrete tanks. Juvenile prawns with an average weight of 1.8 g were stocked into triplicate tanks at densities of 5, 10, 15 and 20 prawns/m², grown for 168 d and fed a 34% tilapia diet. Stocking density had significant effect on prawns. Final mean body weight decreased with the increasing density, being highest at 5 prawns/m² (29.6 9). and lowest at 20 prawns/m² (17.4 g). Total yield increased from 135 g/m² (1,350 kg/ha) at a density of 5 prawns/m² to 261 g/m² (2,610 kg/ha) at density 15/m^z to 245 g/m² (2,450 kg/ha) at 20/m^z. Feed conversion ratios were high and ranged from 3.7 (5 prawns/m²) to 5.6 (20 prawns/m²).
In monosex culture of freshwater prawns stocked in triplicate tanks at a density of 5 prawns/m² for 112 d, the all-male population had the best growth performance and feed conversion ratio, followed by the mixed-sex and all-female populations. The all-male population had 99% marketable prawns (>20 g) with an average yield of 159 g/m² (1,590 kg/ha); the mixed-sex population had 90% marketable prawns and the yield was 135 g/m^z (1,350 kg/ha); and the all-female population had 75% marketable prawns with an average yield of 108 g/m² (1,080 kgha).     

Intensive Culture Potential of Penaeus vannamei

Tank and pond rearing studies were conducted to assess the potential for intensive culture of Penaeus vannamei in South Carolina. Postlarvae were stocked in intensive nursery tanks at 500/ m². Growth and survival were compared for shrimp reared in control fiberglass tanks and in tanks with artificial substrates (fiberglass screen). Addition of substrate improved survival (82% versus 58%), but not growth. Juvenile shrimp (mean weight, 1.3 g) from the nursery trial were stocked into 6 m diameter tanks at densities of 10, 20 and 40/m². Growth rate was inversely related to stocking density, with mean sizes of 33.9, 32.5, and 26.7 g attained at the low, medium, and high densities respectively after 168 days. At harvest, standing crop biomass averaged 225.6, 442.0, and 685.4 g/m² for the three densities. To further test the intensive culture potential, two 0.1 ha ponds were stocked with hatchery-reared postlarvae at densities of approximately 40 and 45/m². The ponds were managed intensively using paddlewheel aerators and water exchange averaging 16–17%/day. The ponds were harvested after 138 and 169 days and yielded 6,010 kg/ha of 16.7 g (mean weight) shrimp and 7,503 kg/ha of 17.9 g shrimp, respectively. Average production was 6,757 kg/ha with a food conversion of 2.51. These data suggest good potential for intensive pond culture of P. vannamei in South Carolina and other areas of the continental United States.     

Growth and Survival of the Australian Red Claw Crayfish Cherax quadricarinatus at Three Densities in Earthen Ponds

Australian red claw crayfish Cherax quadricarinatus were cultured in nine 0.02-ha earthen ponds at densities of l/m², 3/m² and 5/m² for 158 d. Average weight at stocking was 3.2 g. All ponds were provided with a combination of hay and corn silage at a rate of 500 kg/ha per month and a commercial crayfish ration fed at 5%, decreasing to 2% of estimated biomass/d during the growing season. Overall survival rate was 72%, and did not differ among treatments. Final yields and average weights varied significantly with stocking density. Red claw averaged 67 g with an average pond yield of 475 kg/ha at l/m². At 3/m² and 5/m², red claw averaged 48 g and 38 g, respectively, and yielded 1,020 kg/ha and 1,422 kg/ha, respectively.     

The Effect of Five Stocking Densities on Growth and Yield of Red Swamp Crawfish Procambarus clarkii

A 34-day study was conducted to estimate the effect of stocking density on growth, biomass, and yield of harvestable animals in red swamp crawfish, Procambarus clarkii (Girard). Juvenile crawfish were stocked at l, 2, 4, 8, and 16 crawfish per m² into plastic-lined metal pools planted with rice ( Oryza sativa ) with three replicate pools at each density. Crawfish averaged 35 ± 1.5 mm (SE) total length at the time of stocking.
Growth in total length and weight was significantly affected by density ( P < 0.01), ranging from 91.5 mm and 20.7 g for crawfish stocked at 1 per m² to 62.5 mm and 6.3 g for crawfish stocked at 16 per m². The total crawfish biomass ranged from 20.7 g per m² for crawfish stocked at 1 per m² to 88.7 g per m² at 16 per m². The portion of that biomass made up of harvestable sized animals (>75 mm total length) ranged from 100% at 1 per m² to 0.7% at 16 per m². Gross revenues per ha were projected for crawfish yields at each stocking density with and without a graded product.     

Effect of Water Exchange Rate on Production, Water Quality, Effluent Characteristics and Nitrogen Budgets of Intensive Shrimp Ponds

Water exchange is routinely used in shrimp culture. However, there are few, if any, systematic investigations upon which to base exchange rates. Furthermore, environmental impacts of pond effluent threaten to hinder further development of shrimp farming in the U.S. The present study was designed to determine effects of normal (25.0%/d), reduced (2.5%/d) and no (0%/d) water exchange on water quality and production in intensive shrimp ponds stocked with Penaeus setiferus at 44 postlarvae/m². Additional no-exchange ponds were stocked with 22 and 66 postlarvae/m² to explore density effects. Water exchange rates and stocking density influenced most water quality parameters measured, including dissolved oxygen, pH, ammonia, nitrite, nitrate, Kjeldahl nitrogen, soluble orthophosphate, biochemical oxygen demand, phytoplankton and salinity. Reduced-exchange and no-exchange treatments resulted in reduced potential for environmental impact. Mass balance of nitrogen for the system indicates that 13–46% of nitrogen input via feed is lost through nitrification and atmospheric diffusion. Growth and survival were excellent in ponds with normal exchange, reduced exchange, and a combination of low density with no water exchange. A combination of higher stocking density and no water exchange resulted in mass mortalities. Mortalities could not be attributed to a toxic effect of any one water quality parameter. Production was 6,400 kg/ha/crop with moderate stocking density (44/m²) and reduced (2.5%/d) water exchange and 3,200 kg/ha/crop with lower stocking density (22/m²) and no water exchange. Results indicate that typical water exchange rates used in intensive shrimp farms may be drastically reduced resulting in a cost savings to farms and reduced potential for environmental impact from effluent.     

Polyculture of Macrobrachium rosenbergii and Notemigonus crysoleucas

A polyculture study was conducted in southwest Louisiana comparing production of Malaysian prawns, Macrobrachium rosenbergii , in monoculture and polyculture with Golden shiners, Notemigonus crysoleucas .
This test revealed stocking of shiners at 24.7/m² with prawns at 4.4/m² resulted in increased total pond production over monoculture of prawns at 4.4/m² with equal prawn yields in both systems and little increase in labor. Feeding rates were based on prawn biomass. Food conversion ratios ranged from 0.5 to 1.0 in polyculture and 0.9 to 1.1 in monoculture when total production was considered. Prawn production averaged 640 kg/ha in polyculture and 629 kg/ha in monoculture. Mean size of prawns was 19 g in polyculture and 20 g in monoculture. The polyculture of shiners with prawns added an average of 307 kg/ha of the bait fish to pond production.
Shiners did not compete seriously with prawns when stocked at these rates. This practice could result in added revenues to producers culturing these species together.     

Production of Nile Tilapia Oreochromis niloticus and Freshwater Prawn Macrobrachium rosenbergii Stocked at Different Densities in Polyculture Systems in Brazil

Abstract.— The effect of stocking prawns Macrobrachium rosenbergii at increasing densities in ponds with Nile tilapia Oreochromis niloticus reared at low density was evaluated. Twelve 0.01-ha earthen ponds were stocked with 1 tilapia/m² and 0, 2, 4, or 6 postlarvae prawn/m². Three replicates were randomly assigned to each prawn density. Postlarval prawns were stocked a week prior to tilapia juveniles and both were harvested 175 d after the beginning of the experiment. Tilapia final average weight, survival, production, and food conversion rates did not differ significantly among treatments ( P > 0.05); the averages were 531 g, 67%. 3,673 kg/ha, and 1.91, respectively. Prawn survival rates did not differ for the three stocking densities (mean 90%). However, final weight and production were significantly different ( P < 0.05) as follows: 34.0, 23.0, and 14.7 g and 639, 909, and 818 kg/ha, respectively for 2. 4, and 6 prawns/m² densities. Stocking densities up to 6 prawn/m² did not affect tilapia production and required neither additional feeding nor significant changes in management. The polyculture system allowed an increase in total production with the same amount of supplied feed, thus improving the system sustainability.     

Use of duckweed (Lemna sp.) grown in sugarmill effluent for milkfish, Chanos chanos Forskal, production

Abstract. Oxidation treatment of sugarmill waste using duckweed ( Lemna sp.) as part of the system, to reduce effluent nutrient concentrations and biological oxygen demand (BOD), was evaluated during a 6 month milling season in Negros Oriental, Philippines. Mean ammonia concentration in effluent water was reduced from 0·87 to 0·31 mg/l NH₃-N and orthophosphate from 0·93 to 0·51 mg/l P₂O₅, while mean BOD was reduced from 611 to 143mg/t BOD₅, after treatment. Seasonal mass fish kills in the adjoining bay no longer occurred during the 3 years following introduction of this treatment. The mean duckweed production (dry weight) was 8–8g/m²/day. Duckweed was harvested from a 1·9ha area of the system and transferred to an adjacent milkfish, Chanos chanos Forskal, farm. Its fertilization effect, in terms of lablab production ( lablab is the biological complex of bluegreen algae, diatoms, bacteria and various animals which forms a mat at the bottom or floats in patches), was evaluated in the milkfish ponds. This was compared with ponds fertilized with either inorganic fertilizers or cow manure, in the traditional way. Lablab growth was significantly increased using duckweed, with ash-free dry weight production averaging 32g/m²/day following fertilization with duckweed compared with 4g/m²/day using inorganic fertilizers. Milkfish net production averaged 320 kg/ha/90-day crop in inorganically fertilized ponds. 545kg/ha/90-day crop for cow manure and 820kg/ha/90-day crop in duckweed-fertilized ponds. The system is described and the benefits of this integrated waste treatment-fish production facility are discussed.     

Survival of stocked hatchery-reared brown trout, Salmo trutta L., fry in relation to the carrying capacity of a trout nursery stream

Abstract. During the period June 1982-84 hatchery-reared brown trout, Salmo trutta L., fry were Stocked into stretches of the Owendoher. a trout nursery stream on the east coast of Ireland. These experiments were designed to examine the survival of stocked fry and to estimate the carrying capacity of the system. During the first year fry were stocked into sectors already supptorting wild fish at densities normal for the system. In the following year fry numbers were artificially reduced prior to stocking with the hatchery-reared fish. Mortality of the stocked fry was high after release with less than 33% of the fish surviving beyond the first 3 weeks. No stocked fish survived after October 1982. In the second year, however, 2-9% of the fish survived. The best survival rates were achieved where wild fry numbers were lowest. Regardless of the initial stocking density the various experiments yielded autumn fry densities (0.07-0.7 fish/m²) similar to those at unstocked sites (0.1-0.62 fish/m²).
Stocking did not increase recruitment to the 1+ group and again 1+ densities (0.15-0.35 fish/m²) similar to unstocked sites (0.07-0.39 fish/m²) were obtained at the end of each year. These results suggest that spawning and recruitment in the Owendoher yield population densities approaching the maximum carrying capacity of the stream. The system appears to support a maximum summer fry density in the region of 1 fish/m² and a maximum autumn density of 0.7 fish/m².     

Water Quality and Microbial Dynamics in Shrimp Ponds Receiving Bagasse-Based Feed

Pond water quality and associated microbial biomass were studied in relation to the type of feed applied during the culture of the marine shrimp Penaeus vannamei . The feeds tested included conventional feedlot manure as well as two feeds based on bagasse, a sugarcane waste product. Physical and chemical parameters were studied during a 100 day trial in 200 m² earthen ponds. Both bagasse-based feeds supported a significantly larger microbial community as measured by specific biomass numbers ( P < 0.01), ATP content ( P < 0.001) and amount of the particulate organic matter present on pond bottoms ( P < 0.025). For both bagasse-based treatments, the estimated bacterial cell number in the flocculent layer was 3.11 ± 10¹²/m², compared to the much lower cell number of 7.53 ± 10¹⁰/m² for control ponds. Harvest data suggest that bagasse forms a potential base for feeds when applied to extensive shrimp cultures.     

Effects of Population Density and Feeding Rate on Growth and Feed Consumption of Red Swamp Crawfish Procambarns clarkii

Wire-mesh enclosures were used in production ponds to conduct growth trials in which population density and feeding rate were evaluated in a 2 × 2 factorial arrangement for their effects on crawfish growth. Juvenile Procambarus clarkii of uniform size (0.5 g) were stocked at 2 or 20 animals/m² in experiment 1 and weighed biweekly for 12 wk. Rice forage served as the detrital base, and supplemental feed (25% crude protein) was provided at either a low (26–52 kg/ha per week) or high (104–418 kg/ha per week) rate. In experiment 2, mixed sizes of crawfish were stocked at 10/m² or 20/m² and fed the formulated feed at either 52 or 312 kg/ha per week. Feed consumption was estimated for each treatment combination. Only population density significantly affected crawfish growth. Mean weight gain and final weights were inversely proportional to density but only when total crawfish biomass exceeded 1,235 kg/ha. Growth was not significantly influenced by feeding rate, but the high feeding rate resulted in a significantly greater ratio of hepatopancreas weight to body weight and tended to decrease hepatopancreas moisture levels, indicating improved condition. Population density, feeding rate, and their interaction had significant effects on estimated feed consumption. From the simple linear regression of mean feed consumption on crawfish standing crop, it was estimated that crawfish consume about 0.1 kg of dry feed per ha per week per kg of crawfish biomass on a 5 d per week feeding schedule at mean water temperatures, ranging from 14 to 30 C.     

Effects of Diffused Aeration and Stocking Density on Growth, Feed Conversion, and Production of Florida Red Tilapia in Cages

The effects of four levels of diffused aeration (0, 6, 12, and 24 hours/day) and two stocking densities (400 and 600 fish/m³) on the culture performance of caged Florida red tilapia were evaluated in 1 m³ cages in a 2 ha watershed pond on St. Croix, U.S. Virgin Islands. Fish obtained a nutritionally-complete (36% protein), floating feed from demand feeders for 143 to 146 days. Diffused aeration had no significant ( P > 0.05) effect on fish growth, survival, feed conversion, and production in cages. Combined across all levels of diffused aeration, fish stocked at 400/cage had a greater growth rate (2.21 vs. 1.97 g/day), larger final body weight (370 vs. 335 g), and a lower feed conversion ratio (1.69 vs. 1.80) than fish stocked at 600/cage ( P < 0.05). The final biomass of fish stocked at the higher density (181 kg/m³) was greater than at the lower density (140 kg/m³). The enhancement of water exchange rates by diffused aeration did not increase tilapia growth rate or production in cages.     

Preliminary Studies on Stocking Density and Production of Hamoor Epinephelus tauvina in PVC-Lined Raceways

The results of two stocking density trials on the nursery and grow-out stages of Epinephelus tauvina (Family: Serranidae), in PVC-lined raceways are presented.
At the nursery stage, fry of 17.1 g initial mean weight showed no significant differences in growth rate, survival rate and condition factor when stocked at densities of 200 and 400 fish/m³ over a period of 52 days. Fish grew to mean weights of 61.7 and 63.7 g, giving growth rates of 0.86 and 0.90 g/fish/day and final biomasses of 12.1 and 2S.2 kg/m³ for densities of 200 and 400 fish/m³, respectively. Survival rates were excellent for both treatments at 98percnt; or greater. Food conversion efficiency was slightly improved at the higher density.
At the grow-out stage, E. tauvina of mean weights ranging from 150-170 g cultured for a period of 215 days grew better at a density of 5 fish/m³ than at densities of 20 and 60 fish/m³ (final size: 770, 560 and 450 g with growth rates of 2.8, 1.8 and 1.4 g/fish/day, respectively). Survival rates were higher at the two lower densities. Overall, total biomass increased with stocking density (3.9, 11.1 and 23.4 kg/m³, for 5, 20 and 60 fish/m³, respectively). These results indicate that hamoor has potential to be successfully cultured in raceways.     

The Potential Use of Mangrove Forests as Nitrogen Sinks of Shrimp Aquaculture Pond Effluents: The Role of Denitrification

A generalized nitrogen budget was constructed to evaluate the potential role of mangrove sediments as a sink for dissolved inorganic nitrogen (DIN) in shrimp pond effluents. DIN concentrations were measured in pond effluents from three semi-intensive shrimp ponds along the Caribbean coast of Colombia between 1994–1995. Mean NH₄⁺ concentrations in the discharge water for all farms were significantly higher (67 × 12 μg/L) than in the adjacent estuaries (33 × 8 μg/L). Average NH₄⁺ concentrations in the pond discharge over all growout cycles were similar, representing an approximate doubling in relation to estuarine water concentrations. In contrast, NO₂^-+ NO₃^- concentrations were similar in both pond effluent and estuarine waters. Dissolved inorganic nitrogen loading of the ponds was similar. The estimated reduction of DIN in pond effluents by preliminary diversion of outflow to mangrove wetlands rather than directly to estuarine waters would be × 190 mg N/m² per d. Based on this nitrogen loss and depending upon the enrichment rate, between 0.04 to 0.12 ha of mangrove forest is required to completely remove the DIN load from effluents produced by a 1-ha pond.     

Growth of Crawfish Procambarus clarkii as a Function of Density and Food Resources

This study utilized enclosures (cylindrical, 5-mm wire mesh, O.5 m² bottom surface area) placed over rice-forage substrates in experimental crawfish ponds to contain crawfish under typical pond culture conditions. Juvenile Procambarus clarkii were stocked at six densities (2, 4, 6, 10, 14, and 18 crawfish/m²) for 12-wk growth trials in October and again in February. Crawfish relied solely on the detrital food system for their nutritional needs. Supplemental feed was supplied to crawfish in additional enclosures at two of the test densities (2 and 10 crawfish/m²). The commercially formulated feed (25% crude protein) was fed (2.02 g dry feed/m²) 3 d/wk (Monday, Wednesday, Friday). All treatments were replicated with six enclosures. Crawfish growth was inversely correlated to culture density. Mean final weights for crawfish feeding from the detrital-system only were 15.3, 13.8, 11.2, 7.9, 7.2, and 5.8 g for crawfish densities of 2, 4, 6, 8, 10, 14, and 18/m², respectively. Mean final weights for crawfish receiving supplemental feed were 20.7 and 12.4 g for densities of 2 and 10 crawfish/m². When compared with density as a factor influencing growth, feed influenced growth less than density abatement. Supplemental feeding improved crawfish growth in detrital systems an average of 46%, while decreasing initial density improved growth an average of 80.5%.     

Super Intensive Culture of Red-Tailed Shrimp Penaeus penicillatus

Two continuous grow-out experiments of red-tailed shrimp Penueus penicillatus were conducted for one year in a super intensive system with a stocking density of 171 and 286 postlarvae/m², respectively. The postlarval shrimp (Ph_8–12) were cultured in three 0.14 ha earthen ponds with concrete dikes. The shrimp were fed with a commercially prepared feed four times a day. Water quality parameters from the second trial varied as follows: water temperature from 23.0 to 30.4 C, salinity from 15.33 to 21.00 ppt, dissolved oxygen (DO) from 3.47 to 7.34 mg/L, NH₃-N from 0.002 to 0.869 mg/L, nitrite-N from 0.013 to 0.844 mg/L, and nitrate-N from 0.021 to 1.795 mg/L. Ammonia-N increased from 0.022 to 46.110 mg/L, while the pH declined from 8.12 to 7.32. Yield was 4,650 kg/0.42 ha from the first crop in 131 days and 5,160 kg/0.42 ha from the second crop in 141 days. The productivity of this system producing P. penicillatus was 11–12 tons/ha/crop.     

Growth, Survival, Yield, and Size Distributions of Freshwater Prawn Macrobrachium rosenbergii and Tilapia Oreochromis niloticus in Polyculture and Monoculture Systems in Puerto Rico

Abstract.— Tilapia and freshwater prawn production in Puerto Rico for monoculture and polyculture systems were compared. The experiment consisted of three treatments with three replicates each. The stocking rates for the prawn monoculture, fish monoculture and polyculture treatments were respectively: 7 prawns/m², 1 tilapia/M², and 7 prawns with 1 tilapia/ m². The mean stocking size for tilapia and prawn were respectively, 7–8 g and 1–1.3 g. After 145 d of culture, yields and mean weight of tilapia in monoculture and polyculture system were not significantly different. Total yields were 2,942 and 2,769 kg/ha, respectively. Mean weights were 348 g in monoculture and 331 g in polyculture. Yields and mean weight of prawns in monoculture and polyculture were significantly different. Total yields were 1,367 and 951 kg/ha, respectively. Mean weights were 55 g in monoculture and 31 g in polyculture. Total yield in polyculture was 3,720 kg/ha showing an increase over the production separately obtained in prawn and fish monoculture.     

Preliminary study on the production of the tilapia, Oreochromis spilurus (Günther), cultured in seawater cages

Abstract. A preliminary study was conducted to assess the performance of the tilapia, Oreochromis spilurus (Günther), cultured in seawater cages at different stocking densities during the nursing and rearing phases. The stocking densities tested were 200, 400 and 600 fish/m³ during the nursing phase and 100, 200, and 300 fish/m³ during the rearing phase.
In both growth phases, no significant differences (P>0.05) were observed among the different stocking densities on the mean individual final weight, daily growth rate, feed conversion ratio and survival rate. Yields in cages stocked with 400 and 600 fish/m³ during the nursing phase, however, were significantly (P<0.05) higher compared with cages stocked with 200 fish/m³. No significant differences (P>0.05) were observed between 400 and 600 fish/m³. A density of 600/m³ is therefore considered to be optimum for the nursing phase.
Yields of cages during the rearing phase increased significantly (P<0.01) with the increase in stocking density. After grading the fish, however, no significant differences (P>0.05) were observed when only fish bigger than 150g were considered. The occurrence of exophthalmia (cataract) was observed in two of the four replicates at the highest stocking density (300 fish/m³) during the rearing stage. Therefore, a stocking density of 200 fish/m³ is considered optimum for the rearing phase.     

Effects of Water Temperature, Density, and Sex Ratio on the Spawning Rate of Red Claw Crayfish Cherax quadricarinatus (von Martens)

Effects of water temperature on red claw crayfish Cherax quadricarinatus spawning rates was evaluated for 3 mo at 22, 26 and 30 ± 1 C. A 20/m² stocking density and a 1:2 M: F sex ratio was used. Spawning rate increased as temperature increased, with 30 C providing the highest spawning rate ( P < 0.05). Effects of stocking density and sex ratio on the reproduction of red claw crayfish were also evaluated at densities of 10.15 and 20/m², with a sex ratio of 1:1, and at three sex ratios (1:1. 1:3 and 1:5 M: F) at a density 10/m². Water temperature was maintained at 28 ± 1 C and photoperiod was maintained at 14L: 10D for 6 mo during the density and sex ratio experiments. Spawning rates were not significantly different ( P > 0.05) within the three stocking densities at a sex ratio of 1:1, nor were they different ( P > 0.05) for the three sex ratios at a density of 10/m². Results revenled that densities as high as 20/m² and sex ratios of 1 male to 5 females can be used to increase spawning per tank. Also, high temperature (28 ± 1 C) and long day lengths (14L: 10D) can be utilized to stimulate peak spawning rates, but high spawning rates cannot be maintained for more than about 3 mo.