Effects of dietary phenylalanine on growth, digestive and brush border enzyme activities and antioxidant capacity in the hepatopancreas and intestine of young grass carp ( Ctenopharyngodon idella )

This study investigated the effects of phenylalanine on growth, digestive and absorptive ability and antioxidant status of young grass carp ( Ctenopharyngodon idella ). Young grass carp were fed diets containing 3.4 (basal diet), 6.1, 9.1, 11.5, 14.0 and 16.8 g phenylalanine kg −1 diet with a fixed of 10.7 g tyrosine kg −1 diet for 8 weeks. Percent weight gain ( PWG ), feed efficiency and feed intake of fish were the lowest in fish fed the basal diet ( P  <   0.05). Trypsin, lipase and amylase activities in the hepatopancreas, and antioxidants including glutathione contents and glutathione reducase activities in the hepatopancreas and intestine were all the highest in fish fed 11.5 g phenylalanine kg −1 diet ( P  <   0.05). Trypsin, chymotrypsin and amylase activities in whole intestine, and creatine kinase, Na + , K + ‐ ATP ase and alkaline phosphatase activities in the proximal intestine, and superoxide dismutase activities in the hepatopancreas and intestine were all the highest when phenylalanine at level of 9.1 g kg −1 diet ( P  <   0.05). In conclusion, phenylalanine improved growth, digestive and absorptive ability, and antioxidant capacity of young grass carp. The phenylalanine requirement of young grass carp (256–629 g) based on PWG was 10.4 g kg −1 diet or 3.44 g 100 g −1 protein.