Functional Profiles of Fish Gut Microbiota Associated With Feeding Habits in the Midstream of the Jialing River Under Cascade Channelization.

To examine the influence of diet on fish gut microbiota in channelized rivers, we characterized the gut microbial communities of fish with different feeding habits in the midstream of the Jialing River. The main findings are as follows: (1) 16S rRNA gene amplicon sequencing identified Firmicutes and Proteobacteria as the dominant phyla, with their relative abundances differing significantly among fish of distinct feeding habits. Firmicutes exhibited the highest relative abundance in carnivorous fish (93.41%), followed by omnivorous (53.39%) and herbivorous fish (29.3%). In contrast, Proteobacteria was most abundant in herbivorous fish (32.72%), with lower levels in omnivorous (22.43%) and carnivorous fish (4.81%). (2) The Kruskal-Wallis test indicated significant differences in the α-diversity of gut microbial communities among fish with distinct feeding habits (p < 0.05), where herbivorous fish presented the highest α-diversity, followed by omnivorous fish, with carnivorous fish exhibiting the lowest. PERMANOVA analysis showed that the feeding habits significantly influenced gut microbial community structure (Pseudo-F = 3.85, R 2 = 0.18033, p < 0.05). (3) PICRUSt2 functional prediction analysis showed that omnivorous fish in the midstream of the Jialing River had a higher relative abundance of pathways related to microbial metabolism in diverse environments (4.792% ± 0.221%). In comparison, herbivorous fish had a higher relative abundance of pathways related to carbon fixation pathways in prokaryotes (0.927% ± 0.091%). In contrast, carnivorous fish not only had a higher relative abundance of the cysteine and methionine metabolism pathway (1.026% ± 0.051%) but also showed higher relative abundances of pathways related to carbohydrate utilization, including starch and sucrose metabolism (0.768% ± 0.031%) and the phosphotransferase system (PTS) (0.461% ± 0.019%), which may be associated with habitat homogenization following channelization. These findings provide a reference for habitat restoration in channelized rivers and the conservation of fish resources.