Effects of Glutamine Supplementation on Atlantic Salmon Salmo salar Metabolic Performance at High Temperatures

Atlantic salmon are one of the most important fish species in global aquaculture production. However, temperature increases attributed to climatic events impair the production of Atlantic salmon during summer. Additionally, the nutritional requirements for this species when reared under elevated temperatures require elucidation. To address this gap, a feeding trial was conducted to investigate the effect of glutamine supplementation—a functional amino acid (AA) important for energy production and gut health—on the growth, metabolism, gut morphology, antioxidant capacity and thermal tolerance of Atlantic salmon parr at elevated temperatures (22°C). Atlantic salmon were pair-fed three isoenergetic diets: a control diet (D1, no addition of glutamine), D2 (7% glutamine supplementation with other dietary AA levels reduced—isonitrogenous to D1) and D3 (6% glutamine and with the same AA profile as D1). Metabolic rate measurements and sampling commenced after 7.5 weeks on diets and 3 weeks of exposure to 22°C. Glutamine supplementation (D2 and D3) did not affect specific growth rate (SGR), condition factor, relative gut mass or carcass composition despite fish fed D3 having increased pyloric caeca fold height (hF). Resting, maximum and digestive metabolic rates were also unaffected by glutamine supplementation. Contrary to findings in other fish species at optimum temperatures, this study showed that glutamine supplementation did not improve the growth performance of Atlantic salmon parr at elevated temperatures despite enhancing pyloric caeca surface area.