Effects of dietary arginine and glutamine on growth performance, nonspecific immunity, and disease resistance in relation to arginine catabolism in juvenile turbot (Scophthalmus maximus L.)

A 12-week feeding trial was conducted to investigate the effects of dietary arginine (Arg), glutamine (Gln), and their interactions on growth performance, nonspecific immunity, disease resistance, and Arg catabolism in juvenile turbot (Scophthalmus maximus L.). The basal diet was formulated with white fish meal, soybean meal, and corn gluten meal to contain 50% crude protein and 12% crude lipid. Nine isoproteic and isolipidic experimental diets were formulated by supplementing the basal diet with three levels of l-Arg and l-Gln (0.0%, 1.0%, and 2.0% each). Triplicate groups of 35 fish were fed a fixed ration twice daily in an indoor recirculating seawater system. After the feeding trial, fish were challenged by Edwardsiella tarda and survival rate (SR) was recorded for 7 days. The results showed that dietary Arg and Gln levels did not significantly affect growth performance of juvenile turbot (P > 0.05). Respiratory burst activity in head-kidney macrophages increased significantly as dietary Arg or Gln increased (P < 0.05), but no significant interactions was observed (P > 0.05). Significant interactions between dietary Arg and Gln were observed on lysozyme and glutathione peroxidase activity in serum (P < 0.05). There was also a significant interactive effect of dietary Arg and Gln on inducible nitric oxide synthase activity in serum and liver, and arginase I gene expression in liver (P < 0.05). Fish fed diets with the highest Arg and Gln showed significantly higher levels of arginase I gene expression in liver (P < 0.05). After the E. tarda challenge, SR of juvenile turbot were significantly improved as dietary Arg increased (P < 0.05), but no significant effect of dietary Gln and their interactions was observed (P > 0.05). It can be concluded that inclusion of Arg and Gln in the diet did not have a positive effect on growth performance of juvenile turbot, but significantly improved nonspecific immune responses. Dietary Arg and Gln levels also had significantly interactive effects on Arg catabolism. Disease resistance was significantly enhanced with the increasing of dietary Arg.