Dietary chitosan enhances gut microbial diversity and modulates beneficial and pathogenic communities in Channa striata fingerlings.

Dietary modulation of the gut microbiome is a promising approach for improving fish health and sustainability in aquaculture. Chitosan, a biopolymer derived from Artemia shells, has gained attention as a functional prebiotic feed additive due to its antimicrobial and immunomodulatory properties. The effects of dietary chitosan on gut microbial diversity and community composition were evaluated in Channa striata (murrel) fingerlings. Fish were fed three experimental diets: a basal diet (Exp-1), a black soldier fly larvae (BSFL)-based control diet (in which BSFL meal was used as a primary protein ingredient, with its nutritional composition considered during formulation), and a chitosan-supplemented diet (Exp-2). Gut microbiota were characterized using high-throughput 16S rRNA gene sequencing, and microbial diversity, composition, and interaction networks were analyzed. Alpha diversity analysis demonstrated that the chitosan-based diet significantly enhanced microbial richness (Chao1 = 531.62) and promoted a more balanced gut microbial structure compared to the basal diet, which showed reduced diversity and relative dominance of certain taxa previously reported to include opportunistic species. Chitosan supplementation enriched genera such as Lactobacillus, Bacteroides, and Alloprevotella, along with members of Muribaculaceae, which are commonly associated in the literature with functions such as polysaccharide degradation and short-chain fatty acid production, although functional roles cannot be conclusively assigned at the genus level. In contrast, the basal diet group showed a higher abundance of taxa including Plesiomonas and Clostridium sensu stricto, which have been reported in some contexts to include opportunistic strains. Network analysis further revealed stronger clustering and connectivity among microbial taxa under chitosan supplementation, suggesting improved microbial stability. Overall, dietary chitosan appears to influence gut microbial composition and diversity, suggesting a possible role in influencing gut microbial balance. These findings highlight its possible application as a sustainable feed additive in aquaculture, although further functional validation is required.