Effects of Cetobacterium somerae fermentation product on glucose metabolism, gut and liver health of largemouth bass (Micropterus salmoides) fed with high carbohydrate diet

Cetobacterium somerae is an important commensal bacterium in fish with reported benefits on fish glucose metabolism and health. However, the beneficial effects of Cetobacterium somerae have never been investigated in economical fish fed high-carbohydrate diet. In this study, we investigated the effects of dietary supplementation with Cetobacterium somerae fermentation product (CFP) on glucose metabolism, gut and liver health in largemouth bass ( Micropterus salmoides ) fed a high-carbohydrate (HC) diet. Largemouth bass (7.70 ± 0.04 g) were fed with low-carbohydrate (LC) diet, HC diet, or HC diet supplemented with different doses of CFP (0.25%, 0.50%, 1.00%) for 8 weeks. Results showed that although CFP did not significantly affect weight gain or body indices, it markedly alleviated HC-induced metabolic disorders. CFP reduced postprandial blood glucose levels in fish fed HC diet. CFP also reduced hepatic steatosis, as indicated by liver triglyceride (TG) content and histological analysis. Furthermore, CFP reduced serum ALT and AST levels in fish fed HC diet to levels comparable to the LC group. Consistently, CFP supplementation in HC diet reduced the hepatic expression of pro-inflammatory genes ( il-1β , il-8 , tnf-α , nf-κb ) and improved the expression of anti-inflammatory genes ( il-10 , tgf-β ). CFP group improved the expression and activity of antioxidant enzymes and reduced MDA levels in the liver of HC-fed fish. In terms of gut health, CFP improved the expression of tight junction genes and reduced the expression of pro-inflammatory genes in the intestine of fish fed HC diet, and improved intestinal histology of HC-fed fish. Additionally, CFP modulated the gut microbiota, with an enrichment of Firmicutes and a reduction of Proteobacteria. Together, our results demonstrate that Cetobacterium somerae fermentation product improved glucose homeostasis, alleviated hepatic steatosis and injury, and improved intestinal health and intestinal microbiota of largemouth bass fed HC diet, showing promise as a sustainable functional feed additive for the HC formulation of largemouth bass.