A LABORATORY INVESTIGATION OF Macrobrachium rosenbergii NURSERY PRODUCTION1

Three experiments were performed to evaluate the effect of temperature, habitat, and stocking density on the survival and growth of juvenile Macrobrachium rosenbergii. Experiment 1 was initiated with 0.02 g prawns stocked at densities of 900 and 1200 PL/m2 for levels of one and three habitats per tank. Experiment 2 was stocked with 0.01 g prawns at densities of 1200 and 1500 PL/m2 and were maintained at 24 and 28°C. Concurrently, experiment 3 evaluated stocking densities of 150, 300, and 600 PL/m2 at 28°C. Experiments were conducted over a period of 8–10 weeks. Experiments 1 and 2 clearly showed a region where there was a significant increase in mortality rate. It was noted that the onset of the mortality shift, referred to as the breakpoint, generally occurred when the prawns were between 8 and 9 weeks old. The breakpoint was evident at all levels of temperature and habitat, and at stocking densities above 900 prawns/m2. The occurrence of breakpoint did not seem to be related to mean weight or biomass. Percent survival at the end of the experimental periods was generally inversely proportional to the initial stocking density, showing a high of 84% at 150 PL/m2 and a low of 39% at 1500 PL/m2. Overall growth was greater for stocking densities at or below 600 PL/m2 (mean weight gain 0.8–1.0 g) as compared to stocking densities above this point (0.4 g). Growth rate was not significantly different between densities of 1200 and 1500 PL/m2. At 24°C the average survival was 78%, significantly greater than 43% at 28°C. Temperature also significantly increased overall growth, yielding on the average 0.41 g at 28°C versus 0.23 g at 24°C. The number of habitats per tank did not appear to influence survivability, however, growth may be affected by the number of habitats per tank.