Habitat-Associated Variation in Dietary Composition, Gut Microbiota, and Muscle Nutritional Characteristics of Hemibagrus guttatus in a Dam-Regulated River.

Hydropower regulation can alter riverine habitats and potentially influence fish diet, gut microbiota, and nutritional characteristics. In this study, upstream and downstream populations of Hemibagrus guttatus (H. guttatus) were investigated in a dam-regulated reach of the Hongshui River associated with the Datengxia Water Conservancy Project using 12S rRNA and COI metabarcoding, 16S rRNA gene sequencing, and muscle nutritional analyses. Fish from the two habitats exhibited distinct dietary compositions, accompanied by significant differences in gut microbial diversity, community structure, and predicted microbial functions. Upstream fish harbored higher microbial diversity and greater abundances of Firmicutes-associated taxa, including several putatively beneficial bacteria, whereas downstream fish showed enrichment of Proteobacteria-associated taxa and functions related to environmental adaptation. Muscle composition also differed between habitats, with upstream fish containing higher moisture and crude lipid contents and downstream fish exhibiting higher crude protein content. These habitat-associated differences suggest that natural dietary resources and intestinal microbiota are closely linked to host nutritional characteristics. These findings highlight the importance of considering upstream-downstream habitat origin when evaluating the trophic, microbial, and nutritional characteristics of H. guttatus and provide a biological reference for the management and conservation of fish populations in dam-regulated rivers.