Chitosan oligosaccharide enhances growth and immune response in Siniperca chuatsi cultured in recirculating aquaculture systems (RAS) by activating MAPK/NF-κB signaling in the gut-liver axis

Siniperca chuatsi is a high-value carnivorous fish in north-eastern Asia. It often experiences immune suppression and health problems when fish shift from live prey to formulated diets in intensive culture. Chitosan oligosaccharides (COS), a natural immunomodulator, have demonstrated probiotic effects in several aquatic species, but systematic data in carnivore fish remain limited. In this study, the impact of 0.3% COS dietary supplement on growth performance, hepatic gene expression, gut microbial composition, and intestinal metabolite profiles in S. chuatsi has been explored. It was observed that dietary supplementation with 0.3% COS significantly enhanced ( P < 0.05 ) the weight-gain rate. The liver transcriptomic analysis revealed 6506 differentially expressed genes, with 6007 being significantly up-regulated and 499 significantly down-regulated ( P < 0.05 ). KEGG pathway enrichment analysis highlighted the significant involvement of the MAPK and NF-κB signaling pathways. The abundance of probiotic genus Cetobacterium increased dramatically to 54.21%, while 19 potential pathogenic genera, including Klebsiella and Pseudomonas , were significantly suppressed. Simultaneously, the intestinal immunometabolite profile transitioned towards an anti-inflammatory state, as evidenced by a decrease in pro-inflammatory mediators, including leukotriene E4 and arachidonic acid, alongside an increase in anti-inflammatory mediators, such as oleoylethanolamide and 20-carboxy-arachidonic acid. Overall, this study presents the first comprehensive evidence that supplementing feed with 0.3% COS enhanced S. chuatsi growth by improving intestinal microbiota, activating hepatic MAPK-NF-κB signaling pathway through the gut‑liver axis, supporting immune cell survival under inflammatory conditions, and boosting intestinal immune substances. Thus, provides key insights for the use of COS as functional feed additives in S. chuatsi aquaculture. • Dietary 0.3% COS supplementation improves growth performance of S. chuatsi in RAS by 71%. • COS reshapes gut microbiota, enriching Cetobacterium to 54.2% while suppressing 19 pathogenic genera. • COS activates hepatic MAPK/NF-κB signaling and shifts intestinal immunometabolites toward an anti-inflammatory state.