Effects of Population Density on Growth and Survival of Macrobrachium rosenbergii REARED IN RECIRCULATING WATER MANAGEMENT SYSTEMS 1

Growth and survival were monitored among juvenile Macrobrachium rosenbergii (de Man) reared at different population densities in recirculating water management systems. Four cylindrical tanks, each with a bottom area of approximately 2.5 m 2 , and two rectangular raceways with bottoms about 2.8 m 2 in area were used in the experiments. The cylindrical tanks were stocked with 0.12 g prawns at densities of 10 to 200 animals/m 2 of bottom area. Juveniles of similar size were stocked in the raceways at about 200 and 400/m 2 in one study, and slightly smaller animals (0.07 g) were reared at densities approximating 200 and 500/m 2 in a second raceway experiment. Both survival and growth varied inversely with population density in all experiments. After 112 days, a mean weight of 9.2 g and survival rate of 82% were obtained among the prawns stocked at 10/m 2 in a cylindrical tank compared to a mean weight of 3.6 g and survival rate of 50% for those stocked at 200/m 2 . However, survival was good (nearly 80%) even at 200 prawns/m 2 for the first 60 days of the study. Similarly, in the raceways growth was relatively slow at the high population densities tested (200 to 500/m 2 ), but survival was excellent for at least the first 6 weeks of rearing (>93% at 200 and 400/m 2 ; about 83% at 500/m 2 ). Survival rates remained high (≥80%) for up to 90 days at 200/m 2 but had decreased to 56% at 500/m 2 by this time. Substantial variations in prawn sizes and growth rates were observed in all experiments. The degree of variation in size within a cohort, which generally increased with mean size, appeared to be unaffected by population density. This suggests that the marked differences in individual growth rates observed within cohorts may be inherent.