Two experiments at different water-flow conditions and stock densities in the critical 6-week nursery phase determined growth, survival and feed conversion of brown-marble grouper juveniles at 35 Day After Hatching (DAH) with initial mean body weight of 0.045±0.02 g and total mean length of 15.08±0.4 mm. In the first experiment, juveniles of 35 DAH were kept in an 80 L fiberglass tank with the flow-through system for 42 days of the nursery phase at three densities: 1, 3 and 5 ind/L. The highest specific growth rate (P<0.05) and the lowest food conversion ratio (P<0.05) were observed for fish at the 3 ind/L stocking density compared to the other groups. No statistically significant differences (P>0.05) were found in the survival rate of fish groups held in any stocking density. In the second experiment, juveniles of 35 DAH were reared with a re-circulating aquaculture system (RAS) at three densities, 1, 3 and 5 ind/L, to evaluate the effects density has on grouper growth and survival rate in the RAS system, and results were compared with the open flow-through system. No statistically significant differences (P>0.05) were found in total length and body weight between treatments (1, 3, 5 fish/L) in the RAS system, while the weight and total length of the fish reared in open water flow-through conditions were significantly larger (P<0.05) than fish reared in the RAS. This study suggests that optimum stocking density in a flow-through system is 3 fish per liter and flow-through water is preferred to the RAS system.
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