Dietary protein requirement of juvenile mud crab Scylla paramamosain

This experiment was carried out to investigate the optimal dietary protein levels for juvenile Scylla paramamosain. Six isoenergtic and isolipidic semi-purified diets were formulated with graded protein levels, and the final protein concentrations were 32.69%, 38.54%, 42.92%, 49.89%, 52.09% and 60.07%, respectively. Each diet was offered to triplicate groups of 28 mud crabs (initial weight 0.04 +/- 0.001 g, carapace length 3.3 +/- 0.05 mm) for 8 weeks. The results showed that the mud crabs fed diets with 32.69% and 60.07% protein had significantly lower survival than those in other treatments (p < .05). The juvenile mud crab consuming 42.92%, 49.89% and 52.09% dietary protein obtained significantly higher weight gain (WG) and specific growth rate (SGR) than other groups (p < .05). Crude protein content in whole body significantly increased with increasing dietary protein level (p < .05). Crabs fed diet with 49.89% had the lowest hepatic aspartate aminotransferase (AST) activity (p < .05). A relatively higher of hepatic alkaline phosphatase (AKP) activity was observed in groups with 42.92% and 49.89% protein diet (p < .05). The hepatic superoxide dismutase (SOD) activity significantly increased with dietary protein level increasing to 49.89% and leveled off thereafter (p < .05). The EcR mRNA expression level in the eyestalk slightly decreased with increasing protein level to 42.92%, and it then obviously up-regulated with dietary protein content further increasing to 52.09% (p > .05). According to the polynomial regression analysis, 47.06% dietary protein was required for juvenile S. paramamosain to obtain maximum growth rate.