Effects of fermented feed on growth and digestive function of juvenile Chinese mitten crab, Eriocheir sinensis

Fermented feed is widely used in aquaculture for its roles in promoting animal growth, improving water quality, and meeting nutritional requirements. The hepatopancreas is crucial for digestion and absorption of Chinese mitten crab, Eriocheir sinensis . This study evaluated the effects of different proportions of fermented feed (0%, 10%, 20%, 30% and 40%) on the growth performance and digestion of E. sinensis following a 60-day feeding trial. Growth performance, digestive enzyme activities, and expression of digestion-related genes peaked in the 30% fermented feed group, with concurrent increases in hepatopancreatic blister-like and fibrillar cells. Further analyses of hepatopancreas microbiota and metabolomics (0% and 30% groups) revealed that 30% fermented feed maintained microbial community homeostasis and upregulated key metabolic pathways, including aminoacyl-tRNA biosynthesis, biosynthesis of amino acids, and tryptophan metabolism. Spearman correlation analysis revealed that several key differentially expressed metabolites were positively correlated with the presence of major bacterial genera following feeding with 30% fermented feed. These findings indicate that the intake of fermented feed may benefit hepatopancreatic physiological homeostasis in juvenile E. sinensis by enhancing growth performance and digestive and metabolic functions, and 30% fermented feed had the best effect by regulating hepatopancreatic microbial communities and metabolic pathways.