Effects of mannan oligosaccharides (MOS) on glucose and lipid metabolism of largemouth bass (Micropterus salmoides) fed with high carbohydrate diet

The application of high-level of carbohydrates is regarded as an efficient way to promote “protein-sparing effects” in aquafeed, but the utilization efficiency of carbohydrates is poor in carnivorous fish. Alleviating the negative effects induced by high carbohydrate diet, including hyperglycemia and hepatosteatosis, is important for the rapid development of aquaculture. In this study, we aimed to explore the effects of mannan oligosaccharides (MOS) on metabolic disorders induced by high-carbohydrate diet in largemouth bass (Micropterus salmoides). Largemouth bass (13.64 ± 0.12 g) were supplied with 8 % carbohydrate (CON), 18 % carbohydrate (HC) and 18 % carbohydrate + 5 g/kg MOS (HM) diets for ten weeks. High carbohydrate diet significantly decreased the weight gain of largemouth bass (P < 0.05), while supplementation of MOS in high carbohydrate diet had no effect on weight gain compared with HC group. Dietary MOS significantly decreased the content of total lipid in the body compared to the HC group (P < 0.05). Addition of MOS significantly increased serum glucose (P < 0.05) but had no effect on the enzyme activity related to glycolysis and gluconeogenesis. Dietary MOS decreased the content of TG in liver by inhibiting the expression of genes correlated with lipolysis. In addition, dietary MOS alleviated liver fibrosis induced by high-carbohydrate diet in largemouth bass. Collectively, our study indicated that dietary MOS supplemented in high carbohydrate diet could improve the liver health in largemouth bass, but it did not alleviate the glucose metabolism disorders. In general, the different effects of prebiotics on metabolism should be considered when prebiotics were applied in aquaculture.