Effects of dietary arginine levels on protein deposition and related immune gene expression in Epinephelus coioides

A 10-week feeding trial was conducted to investigate the effects of dietary arginine levels on the growth performance and immunity of Epinephelus coioides. Seven isonitrogenous and isolipid diets were formulated with arginine contents of 2.13%, 2.42%, 2.71%, 2.95%, 3.20%, 3.48% and 3.74% (dry matter) respectively. Randomly selected healthy groupers initial weight (80.11±0.03) g were divided into 7 groups, with 3 replicates in each group and 25 fish per replicate. It was found that the weight gain rate (WGR) and specific growth rate (SGR) of 2.71% group were significantly higher than 2.13% and 2.42% groups, and the feed coefficient (FCR) was significantly lower than that 2.13% group. The protein efficiency rate of the 2.71% group was significantly higher than those of 2.13% and 3.48% groups, and the protein deposition rate of the 2.71% group was not significantly different from that of 2.95% group, which was significantly higher than that of other groups. Broken-line model analysis of weight growth rate against dietary arginine levels indicated that the optimum requirement of arginine for maximum growth of subadult grouper was 2.73%, corresponding to 5.40% of dietary protein on a dry weight basis. There was no significant difference between 3.20% serum insulin (INS) and 3.48% groups, which were significantly higher than other groups. The level of TOR gene in muscle of 3.48% group was significantly higher than those of 2.13%, 2.42% and 2.71% groups. The expression of b^0,+ AT gene in the hindgut of 2.42% group was the highest, which was significantly higher than that of other groups. There was no significant difference in the expression of b^0,+ AT gene of kidney between 2.95% and 3.20% groups, which was significantly higher than that of other groups. In conclusion, the appropriate level of feed arginine can stimulate the secretion of IGF-I of E. coioides to promote the synthesis of protein and improve the expression of immune genes of the intestine, kidney and liver of fish to improve the body immunity, and ultimately promote the growth of fish.