Regulatory Effects of Myo-Inositol on Carbohydrate Metabolism and Low-Salinity Adaptation in Pacific White Shrimp (Penaeus vannamei)

This study investigated how dietary myo-inositol affects osmoregulation, carbohydrate and lipid metabolism, immunity, and antioxidant properties in Penaeus vannamei under long-term low-salinity conditions. A two-factor (2 × 3) orthogonal approach was used with three different concentrations of dietary myo-inositol (0, 1,200, and 2,000 mg/kg) at two dietary carbohydrate levels: normal carbohydrate or high carbohydrate (HC). Six experimental diets were formulated, and a feeding trial was carried out for 42 days. The interaction of myo-inositol with an HC diet significantly improved shrimp survival, weight gain, and specific growth rates. Dietary myo-inositol increased the contents of Na⁺, K⁺, and Ca²⁺ in the serum and reduced the ion loss caused by low-salinity stress. In addition, a lack of myo-inositol can lead to loosening of gill filament connections and thinning or disappearance of the cuticle. However, myo-inositol supplementation protected the structural and functional integrity of the shrimp gills and significantly enhanced the ion transport capacity (P < 0.05). Two-factor analysis showed that myo-inositol concentration was affected by dietary carbohydrate levels, and an HC diet enhanced myo-inositol biosynthesis in shrimp gills (P < 0.05). The concentrations of myo-inositol are highest in the gills and lowest in the liver and pancreas. Moreover, dietary myo-inositol can improve the immune function and antioxidant capacity of P. vannamei. The results also indicated that under sustained low-salinity stress, high levels of carbohydrates cannot relieve the stress caused by low-salinity conditions and can even affect the healthy growth of P. vannamei. Under HC levels, adding dietary myo-inositol significantly improved glycogen and lipid deposition in hepatopancreas tissue and enhanced carbohydrate utilization and osmotic adjustment ability in P. vannamei under chronic low-salinity stress.