Effects of arginine family amino acids supplementation on growth, whole-body amino acid profiles, antioxidant capacity, and gene expression of juvenile largemouth bass (Micropterus salmoides)

This study investigated the effects of arginine family amino acids supplementation on growth, whole-body amino acid profiles, antioxidant capacity, and gene expression of juvenile largemouth bass (9.43 ± 0.13 g). Five isonitrogenous and isolipidic diets were formulated, using 24% fish meal and 15% casein as primary protein sources, supplemented with 5.75% alanine, 2.84% arginine, 12.75% glutamic acid, 5.01% proline, and 0.74% citrulline (dry matter). Each diet was randomly allocated to three tanks (300L) containing 15 fish, and the fish were fed to satiation twice daily. After 8 weeks of feeding, the glutamic acid group showed significantly lower weight gain (WG; P < 0.05) than the alanine group. The hepatosomatic index of the proline group was significantly increased than that of the alanine group (P < 0.05). Compared to the alanine group, adding arginine and citrulline significantly increased the whole-body arginine concentration of largemouth bass (P < 0.05). The retention rates of branched-chain amino acids (leucine, isoleucine, valine), glutamic acid, aspartic acid, and lysine in fish of the arginine and citrulline groups were significantly reduced (P < 0.05). The liver arginase activity and urea cycle-related enzyme mRNA expression levels in the citrulline group were significantly higher than those in the alanine group (P < 0.05). The citrulline group increased the activity of total nitric oxide synthase, total antioxidant capacity, and superoxide dismutase activities than the alanine group. The concentrations of glutathione in both the arginine group and citrulline group were markedly elevated compared to those in the other groups (P < 0.05). Malondialdehyde content was significantly higher in the proline group than in the other groups (P < 0.05). Although citrulline was not helpful in improving growth performance in this study, it played an important role in improving antioxidant capacity and endogenous synthesis of arginine. These findings indicated that citrulline is an effective arginine alternative for maintaining fish health.