Dietary arginine levels affect growth performance, intestinal antioxidant capacity and immune responses in largemouth bass (Micropterus salmoides)

Abstract

This study explored the role of dietary arginine level (DAL) on growth, intestinal antioxidant status and immune response in juvenile largemouth bass (Micropterus salmoides), providing guidance for the optimization of commercial feed in largemouth bass. Six graded arginine levels in diets were fed to the fish for 8 weeks (1.96%, 2.28%, 2.52%, 2.81%, 3.09% and 3.35% diets). The findings were as follows: with increasing DALs, FW, WG and SGR increased first and decreased, and FCR showed the opposite trend. There was no difference in the contents of crude protein and ash among graded DAL (P > 0.05). DAL (3.09% and 3.35%) significantly increased the activities of plasma AST (P < 0.05). Certain range of dietary arginine levels could improve antioxidant ability by regulating intestinal antioxidant-related parameters including the activities of SOD, GPx, and the contents of GSH and MDA. The gene expression of Nrf2 was significantly increased in response to 2.52% DAL, while Keap1 expression was decreased (P < 0.05). Furthermore, 1.96% and 2.28% DALs significantly increased the gene expression of CAT and GPx (P < 0.05), and SOD expression was the highest in response to 2.52% and 2.81% DALs (P < 0.05). Compared with the control group, the relative expressions of IL-1β, IL-8, TNF-α and NF-κB were reduced that were fed 2.52%− 3.35% DALs. Moreover, the relative expression of IL-10 and TGF-β were peaked in response to 2.81% DAL (P < 0.05). The quadratic regression curve analysis according to the growth results of SGR and FCR, the expressions of IL-10 and TGF-β showed that the optimal dietary arginine requirement for largemouth bass were 2.40%− 2.63% (5.03%−5.46% of dietary protein), and could promote growth, intestinal antioxidant capacity and immune responses in juvenile largemouth bass.