Effects of Different Carbohydrate Level Diets on Growth Performance and Glycometabolism in Mandarin Fish (Siniperca chuatsi) Under Saline-Alkali Stresses

Saline-alkali cultivation is a crucial approach to alleviate the fresh water crisis. However, prolonged saline-alkali stresses might bring adverse effects on fish growth, health, and even death. This study evaluated the effects of different carbohydrate supplementation on growth performance, carbohydrate metabolism, antioxidant capacity, and tissue morphology of mandarin fish (Siniperca chuatsi) under saline-alkali stress. Fish with an initial weight of 31.03 ± 0.12 g, were fed with three carbohydrate levels (8%, 13%, and 18%) in either a freshwater or a saline-alkali water environment (salinity = 6, alkalinity = 0.7 g/L). Results indicated that fish cultured in saline-alkali water performed a higher specific growth rate (SGR) and weight gain (WG). In addition, the activities of the glycolysis pathway, pentose phosphate pathway, and gluconeogenesis pathway were enhanced prominently under this stress. The growth performances were also improved significantly by the increased carbohydrate diets. However, the activities of amylase were inhibited with the increased carbohydrate intake, which impeded the process of glycometabolism. In contrast, the pentose phosphate pathway and gluconeogenesis pathway responded positively to dietary carbohydrate levels, especially under saline-alkali stresses. Moreover, improving the carbohydrate level appropriately could significantly reduce the accumulation of malondialdehyde, promote the activities of superoxide dismutase, and total antioxidant capacity under saline-alkali stress. Furthermore, the expression of insulin receptors showed an ascending tendency in freshwater, while opposite in saline-alkali water with increased carbohydrate intake. In summary, an appropriate saline-alkali environment was more conducive to the growth of mandarin fish. Moreover, 13% carbohydrate diets could enhance its growth performance in saline-alkali environments. It was noteworthy that the effects of insulin on the regulation of carbohydrate metabolism might not be the same as normal conditions during the adaptation process in mandarin fish. The pentose phosphate pathway played a critical part in osmoregulation under saline-alkali stress.