Growth, Development, and Survival of Portunus pelagicus Larvae and Juveniles in Different Feed Regimens, Rearing Media, and Stocking Densities

Various factors in P. pelagicus seed production and grow-out culture were investigated in this study. Experiments were conducted to 1) compare natural and artificial feeds for larval production, 2) evaluate indoor tank and outdoor net cages as rearing media, and 3) assess different stocking densities for grow-out culture. Growth, development, and survival were assessed for the performance of each variable. (I) In larval production, the development of megalopa larvae into crab instar was synchronous in both natural and artificial feed treatments in a 5-day rearing observation. Crab instars began to appear on Day 4 with 27% composition in both feeds. Although survival appeared to be relatively higher in natural feed (43.96 ± 6.04%), this was not significant from survival in artificial feed treatment (33.33 ± 13.34), (t = 0.726, p > 0.05). (II) In Phase I grow-out culture, a two-variable design experiment was conducted to assess growth performance and survival of crab juveniles reared in indoor tanks and outdoor net cages at different stocking densities. Specific growth rate (SGR) differed significantly (t = 2.937, p < 0.05) between indoor tanks (6.39 ± 0.24%.d-1) and outdoor net cages (8.31 ± 1.11%.d-1). However, mean survival rate was better in indoor tanks (20.83 ± 9.24%) than outdoor net cages (8.94 ± 3.58% only), (t = 2.938, p = 0.015). In terms of stocking density, SGR was highest in 75 ind.m-2 (7.87 ± 2.44%.d-1). However, growth performance and survival of juveniles among different stocking densities were not significantly different (p > 0.05). Furthermore, two-factor ANOVA results have shown that growth performance of the juveniles was influenced by both the differences in rearing medium and stocking density, but not in terms of survival (F = 0.120, p = 0.888). (III) In Phase II grow-out culture, juveniles attained highest SGR (3.54 ± 0.56%.d-1) at 5 ind.m-2 stocking density. This was followed by 15 ind.m-2 (3.45 ± 2.39%.d-1) and by 10 ind.m-2 (2.33 ± 0.50%.d-1) (p > 0.05). However, survival rate was highest in 15 ind.m-2 (46.67 ± 0.00%), but the differences among other stocking densities were not statistically significant (p > 0.05). Overall, results suggest that artificial feed can be an alternative for Artemia in rearing megalopae to crab instar stage. Stocking density in Phase I and II grow-out culture did not substantially affect growth performance and survival of juvenile P. pelagicus. However, higher stocking density increases incidence of cannibalism among reared crabs.