Dietary glutamine supplementation improves the osmoregulatory capacity and reduces oxidative stress induced by hyperosmotic stress in Nile tilapia (Oreochromis niloticus)

This study investigated the effects of dietary glutamine on growth performance, antioxidant capacity, and osmoregulation in euryhaline fish (Oreochromis niloticus) under hyperosmotic stress. Nile tilapia was fed four diets with varying glutamine concentrations (0%, 0.75%, 1.5 %, and 3 %) at 0 or 16 ppt for 42 days. The results demonstrated that dietary supplementation of 0.75 % glutamine significantly enhanced the growth performance of Nile tilapia under both 0 ppt and 16 ppt salinity. Hyperosmotic stress significantly reduced the crude protein and crude lipid contents while elevated the ash content of the fish. Under hyperosmotic stress, dietary glutamine supplementation significantly increased the antioxidant and immune capacities, and attenuated apoptosis in the liver of tilapia. The expression of ion transporter genes in the gills and kidneys were both significantly increased by dietary glutamine. Meanwhile, glutamine supplementation significantly reduced the levels of inorganic ions in serum while increased serum osmolality. Hyperosmotic stress significantly activated the glycolysis, gluconeogenesis, and pentose phosphate pathways in the liver of tilapia. However, supplementation of glutamine under hyperosmotic stress would significantly enhance the ability of gluconeogenesis of tilapia in the liver. The results of this research suggested that dietary glutamine might promote the growth performance of fish by enhancing their antioxidant capacity and osmoregulation capacity under chronic hyperosmotic stress. This work investigates the role of glutamine in osmolarity regulation and extends the understanding of its mechanism of action, which could provide a reference for hyperosmotic adaptation in aquatic animals.