Effects of dietary Astragalus membranaceus extract and fucoidan on growth performance, hepatic resilience, antioxidant defense and gut homeostasis of largemouth bass (Micropterus salmoides)

This study aimed to evaluate the individual and combined effects of dietary Astragalus membranaceus extract (AME) and fucoidan on growth performance, hepatic function, antioxidant capacity, intestinal integrity, and gut microbiota in largemouth bass ( Micropterus salmoides ). During a 60-day feeding trial, dietary AME significantly increased weight gain rate (WGR), decreased serum ALT, AST, TG, TC, and LDL-c levels, and enhanced nonspecific immune responses (ACP, AKP, LZM). It also strengthened systemic antioxidant defenses, as evidenced by elevated SOD and CAT activities and reduced MDA in serum, liver, and spleen. Importantly, these beneficial effects were further potentiated when AME was co-administered with fucoidan at graded supplementation levels. Moreover, intestinal tissue morphology and digestive function were found to be significantly improved, as indicated by enhanced villi length, mucosal and muscular thickness, and elevated digestive enzyme activities. Notably, 16S rRNA sequencing revealed a decreased abundance of potential pathogenic genera ( Mycoplasma, Pseudomonas ) and an increased enrichment of beneficial taxa ( Prevotella, Faecalibacterium ), with a trend toward greater microbial richness and diversity. Furthermore, in a copper sulfate-induced acute liver injury model, the AME-fucoidan combination markedly alleviated hepatic dysfunction, improved liver histopathology, reduced lipid deposition, and restored redox homeostasis, accompanied by consistent regulation of related gene expression. Overall, AME and fucoidan exert significant hepatoprotective, antioxidative, immunomodulatory, and gut-protective effects, offering a promising nutritional strategy to enhance fish health and resilience in intensive aquaculture and chemical-induced stress conditions. • AME or combined with fucoidan enhanced growth, hepatic function and systemic antioxidant capacity in largemouth bass. • Dietary AME-fucoidan supplementation reinforced immunity and improved intestinal morphology. • Dietary AME-fucoidan supplementation modulated gut microbiota, increasing beneficial taxa and reducing pathogenic genera. • Dietary AME-fucoidan supplementation effectively alleviated copper sulfate-induced acute hepatic injury.