Myo-inositol improves osmoregulation by promoting lipid utilization in Nile tilapia (Oreochromis niloticus)

This research explores the influence of myo-inositol (MI) on the hypertonic stress adaptation of Nile tilapia (Oreochromis niloticus) by increasing lipid utilization under long-term salinity stress. A two-factor interactive experiment was used, and diets containing either normal lipids (NL, 7%) or high lipids (HL, 15%) contained three MI concentrations of 0, 400, and 1200 mg/kg in each lipid diet. Fish were fed six diets under 20 psu (practical salinity units [psu]) for eight weeks. Under long-term hypertonic stress, dietary MI supplementation significantly improved the growth performance of O. niloticus (P < 0.05). Dietary 1200 mg/kg MI supplementation significantly promoted protein deposition and reduced fat accumulation in the whole fish (P < 0.05). The HL diet significantly caused lipid accumulation in the liver, while dietary 1200 mg/kg MI addition alleviated lipid accumulation by promoting the expression of genes related to lipolysis (PPAR-α; ATGL and CPT) and inhibiting the expression of genes related to lipid synthesis (SREBP; DGAT and FAS) (P < 0.05). In addition, 400 mg/kg MI significantly reduced serum lipids (TG and LDL-C) (P < 0.05). qPCR showed that the purity of dietary 1200 mg/kg MI significantly upregulated the expression of an ion transporter-related gene (NKA) in gills (P < 0.05). Meanwhile, 400 mg/kg and 1200 mg/kg MI significantly affected the content of fatty acids in the liver and gill (P < 0.05). In addition, dietary 1200 mg/kg MI supplementation significantly increased the antioxidant capacity in the liver of O. niloticus. In conclusion, dietary supplementation with 1200 mg/kg MI could regulate lipid metabolism, promote lipid utilization and improve the osmotic regulation ability of O. niloticus.