Dietary arginine affects growth performance, plasma amino acid contents and gene expressions of the TOR signaling pathway in juvenile blunt snout bream, Megalobrama amblycephala

An 8-week feeding trial was conducted to estimate the dietary arginine requirement and investigate the effects of dietary arginine levels on the growth performance, plasma essential amino acids contents and relative gene expressions of target of rapamycin (TOR) signaling pathway in juvenile blunt snout bream. Fish (initial weight: 20.0±0.03g) were randomly sorted into 18 cages (1m×1m×1m) and each cage was stocked with 20 fish for farm pond culture. Six isonitrogenous and isoenergetic practical diets were formulated to contain graded arginine levels ranging from 0.87% to 2.70% of dry diet. At the end of the feeding trial, results showed that final weight (FW), weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) increased with increasing dietary arginine level up to 1.62%, and thereafter showed a decreasing trend, while feed conversion ratio (FCR) showed a converse trend. The hepatosomatic index (HSI) in the fish fed with 2.31 and 2.70% arginine diets were significantly higher than the other arginine diets. Viscerosomatic index (VSI) in the fish fed with 1.62 and 1.96% arginine diets were significantly lower than 0.87, 2.31 and 2.70% arginine diets. The highest whole body protein, lipid and lowest moisture contents were observed in fish fed with 1.96% dietary arginine compared to those fed with the other diets. Plasma arginine content increased with increasing dietary arginine level, whereas plasma lysine decreased with increasing dietary arginine level. Plasma histidine, isoleucine, valine, tryptophan and methionine contents were significantly affected by dietary arginine levels. Relative expression levels of TOR mRNA in the group fed with 1.96% dietary arginine was significantly higher compared to those fed with 0.87 and 1.22% arginine diets. Relative expression levels of insulin like growth factor-1 (IGF-1) mRNA in the groups fed with 1.62 and 1.96% dietary arginine were significantly higher than those fed with the other arginine diets. Significantly higher relative expression levels of ribosomal protein S6 kinase-polypeptide 1 (S6K1) mRNA were found in fish fed with 2.31 and 2.70% arginine diets. Based on FCR and SGR, the optimal dietary arginine level was determined to be 1.85% of diet (5.60% of dietary protein) and 1.84% of diet (5.58% of dietary protein), respectively, using quadratic regression analysis. The findings showed dietary arginine affected growth, plasma amino acid concentration, and gene expressions of TOR signa