Dietary Leucine Requirement and Its Effects on Growth, Immunity, Antioxidant Capacity and Protein Metabolism in Pacific White Shrimp, Penaeus vannamei.

This study was conducted to determine an optimal dietary leucine (Leu) level for Penaeus vannamei by assessing growth, non-specific immune response, antioxidant capacity, digestive enzyme activity and protein metabolism-related gene expression. A basal (L0) diet was formulated without supplemental Leu. Five other diets were formulated supplementing Leu into L0 diet at 5, 10, 15, 20 and 25 g/kg (designated as L5, L10, L15, L20 and L25, respectively). Total of 480 shrimp were randomly distributed into 24 tanks (240 L) in quadruplicate groups per dietary treatment. Growth performance was significantly higher in L5 and L15 groups than in L0 group. Non-specific immune responses were significantly increased in Leu-supplemented groups than in L0 group. Muscle Leu concentration was significantly higher in all Leu-supplemented groups compared with L0 group. Catalase activity was significantly higher in L20 group than in L0 group. Glutathione peroxidase activity was significantly increased in L10 group than in L0 group. Superoxide dismutase activity was significantly increased in all Leu-supplemented groups than in L0 group. Compared to L0 group, dietary Leu supplementation significantly decreased the level of malondialdehyde. Activities of trypsin and lipase were significantly higher in all Leu-supplemented groups than in L0 group. Chymotrypsin activity was significantly higher in L10 group than in all other groups. All Leu-supplemented groups exhibited higher relative gene expression of TOR, S6K and Nrf2 compared to L0 group. 4E-BP was significantly upregulated in L5, L10, L20 and L25 groups than in L0 group. These results indicate that the dietary Leu requirement for maximum weight gain of P. vannamei is 10.6 g/kg.