Dietary arginine requirement for gibel carp (Carassis auratus gibelio var. CAS III) reduces with fish size from 50 g to 150 g associated with modulation of genes involved in TOR signaling pathway

Abstract

A 56-day growth experiment was conducted in net cages to investigate the dietary arginine requirement in two sizes of gibel carp using diets containing casein and precoated crystalline amino acids (CAA) as the main protein sources. Six isonitrogenous and isoenergetic (310g crude protein and 16.8MJ gross energy kg−1 dry matter) diets containing graded levels of arginine from 5.4 to 26.6gkg−1 dry matter were prepared. Triplicates of 30 fish (body weight 51.6±0.3g) or 20 fish (body weight 147.8±0.5g) were fed to apparent satiation with one of six experimental diets by hand four times a day. Specific growth rate (SGR) and feed efficiency (FE) significantly increased with the increase of dietary arginine levels from 5.4 to 17.6gkg−1 (small fish) or from 5.4 to 13.0gkg−1 (big fish), and thereafter, kept constant. In the fish of two sizes, with increasing of dietary arginine level, whole body and dorsal muscle protein content first significantly increased, and then reached a plateau or slightly declined. Protein retention efficiency (PRE) showed the same trend with protein content in big fish, but not in small fish. Muscle arginine contents markedly increased with increasing dietary arginine level in two sizes of fish. Growth hormone (GH), insulin like growth factor-I (IGF-I) and nitro oxide (NO) concentrations in plasma, and NO synthase (T-NOS), arginase activities in liver were affected by dietary arginine levels, while plasma ammonia, urea concentration and hepatic alanine aminotransferase (ALT), aspartate aminotransferase (AST) activities had no significant differences in the fish of two sizes. TOR, S6K1 and IGF-I mRNA in liver or muscle of 5.4gkg−1 group significantly down-regulated, but no differences were found for 4E-BP2 mRNA levels in the fish of two sizes. Pituitary GH mRNA significantly up-regulated with increasing dietary arginine level in small fish, but not in big fish. For the fish of two sizes, significant differences were found in all indices mentioned above except for plasma urea, hepatic ALT and AST. Broken-line regression analysis of SGR demonstrated that dietary arginine requirement for gibel carp of these two sizes were 16.4 (small fish) and 12.9gkg−1 (big fish) of dry matter, corresponding to 53 and 42gkg−1 of dietary protein, respectively.