Inulin alleviates adverse metabolic syndrome and regulates intestinal microbiota composition in Nile Tilapia (Oreochromis niloticus) fed with high-carbohydrate diet.

High carbohydrate diet could achieve protein sparing effect, but it may cause negative impacts on the growth condition of fish due to their poor utilization ability of carbohydrate. How to reduce the adverse effects caused by high carbohydrate diet is important for the development of aquaculture. In the present study, we aimed to identify whether inulin could attenuate metabolic syndrome caused by high-carbohydrate diet in fish. Nile tilapia (Oreochromis niloticus) (1.19 ± 0.01 g) were supplied with 35% carbohydrate (CON), 45% carbohydrate (HC) and 45% carbohydrate + 5g/kg inulin (HCI) diets for ten weeks. The results showed that addition of inulin improved the survival rate when fish were challenged with Aeromonas hydrophila, indicating inulin had an immunostimulatory effect. Compared with HC group, HCI group had lower lipid accumulation in liver and the gene expression analyses indicated that addition of inulin downregulated genes related to lipogenesis and upregulated genes relevant to β-oxidation significantly (P < 0.05). Higher liver glycogen and glucose tolerance were found in HCI group compared with HC group (P < 0.05). These results indicated that inulin could alleviate the metabolic syndrome induced by high-carbohydrate diet. Furthermore, addition of inulin in high-carbohydrate diet changed the intestinal bacterial composition and significantly increased the concentration of acetic acid and propionic acid in fish gut which have the potential to increase pathogen resistance and regulate metabolic characteristics in fish. Collectively, our results demonstrated a possible causal role for the gut microbiome in metabolic improvements induced by inulin in fish.