Adult Atlantic salmon (Salmo salar L.) adapts to long-term surplus dietary arginine supplementation

The current study aimed to investigate the effect of surplus dietary arginine on polyamine and amino acid metabolism and accretion of proteins and lipids, as previous studies have demonstrated a lipid-reducing effect following surplus arginine supplementation in viscera as well as increased muscle growth. Four plant protein-based diets were given increasing concentrations of L-arginine, from 21.1 to 36.1gkg(-1) DM, and fed to quadruplicate tanks of adult Atlantic salmon (1.1kg) for 12weeks. No effects on growth or deposition of fat or protein were observed. Free amino acid concentrations and related metabolites were unaffected in the liver, except for urea, while concentrations in muscle and plasma reflected production of arginine metabolites. Polyamine concentrations were unaffected in liver, muscle and white adipose tissue (WAT), as were the abundance and activity of spermidine/spermine N1-acetyltransferase (SSAT), the rate-limiting enzyme in polyamine turnover. Gene expression demonstrated differential regulation of ornithine decarboxylase (ODC) in liver and WAT, although overall little effects were observed on gene expression. Liver S-adenosylmethionine (SAM) concentrations decreased with arginine supplementation. We suggest that adult Atlantic salmon have adapted to surplus arginine, and the main long-term effect appears to be increased concentrations of arginine metabolites.