Effects of dietary arginine levels on growth, intestinal peptide and amino acid transporters, and gene expressions of the TOR signaling pathway in tiger puffer, Takifugu rubripes

Abstract

This study aimed to determine the dietary arginine requirement of tiger puffer (Takifugu rubripes), and to assess the effect of dietary arginine levels on intestinal peptide and amino acid transporters, and target of rapamycin (TOR) signaling pathway in muscle. Six experimental diets were formulated to contain 480 g kg−1 crude protein from fishmeal, corn protein concentrate and crystalline amino acid premix with graded levels of arginine (19.1, 21.5, 24.4, 26.7, 30.0 and 32.5 g kg−1 of dry diet). Each diet was randomly fed to triplicate groups of 25 fish (an average initial body weight of 19.97 g) per tank. Final body weight, specific growth rate (SGR), feed efficiency ratio, protein efficiency ratio and protein productive value increased with the increase of dietary arginine levels from 19.1 to 24.4 g kg−1 (p < 0.05), and then showed a declining trend although there was no significant difference. With the increase of dietary arginine levels, intestinal oligopeptide transporter 1 (PepT1), cationic amino acid transporter 1 (CAT1) and y+ L-type amino acid transporter 2 (y+LAT2) mRNA levels increased at first and thereafter showed a decreasing trend, where a break point was observed in the 24.4 g kg−1 arginine group. The expression of b0,+-type amino acid transporter (b0,+AT) in intestine was significantly higher in the 21.5 and 24.4 g kg−1 arginine groups compared with the 32.5 g kg−1 arginine group (p < 0.05). Gene expressions of TOR, ribosomal protein S6 kinase 1 and eukaryotic translation initiation factor 4E-binding protein 1 in muscle were not statistically different in all treatment groups (p > 0.05). In conclusion, an optimal level of dietary arginine stimulated intestinal peptide and amino acid transporters, while gene expressions of TOR signaling pathway in muscle were not responsive to dietary arginine levels. Based on nonlinear regression analysis of SGR, the dietary arginine requirement of tiger puffer was estimated to be 24.40 g kg−1 of dry diet (50.12 g kg−1 of dietary protein).