High-throughput 16S rRNA sequencing reveals gut dysbiosis and linked hepatic toxicity in triflumezopyrim treated juvenile freshwater fish Labeo rohita.

Triflumezopyrim (TFM), a mesoionic insecticide widely applied in rice cultivation, poses a potential threat to non-target aquatic organisms. This study evaluated the impact of chronic sub-lethal TFM exposure 0 ppm (Control), 1.41 ppm (LSC), and 4.97 ppm (HSC) on the intestinal microbiota of juvenile rohu (Labeo rohita) over 21 days. 16 S rRNA gene amplicon sequencing analysis identified Proteobacteria, Actinobacteria, and Firmicutes as the dominant phyla. Pesticide exposure induced significant gut dysbiosis: Actinobacteria were decreased by 56.5%, whereas Proteobacteria increased by 105.14% in TFM-treated groups. While alpha diversity remained stable, Non-metric Multidimensional Scaling (NMDS) revealed distinct microbial clustering, indicating significant structural shifts in community composition. Pearson's correlation analysis linked these microbial shifts to host biochemical indices; beneficial genera such as Rhodobacter and Cetobacterium correlated positively with antioxidant enzyme activity and negatively with aspartate aminotransferase (AST). Furthermore, KEGG-based functional profiling showed a predicted enrichment of xenobiotic degradation pathways in treated fish. Specifically, higher read abundances were observed for omega transaminase (EC 2.6.1.18), alcohol dehydrogenase (EC 1.1.1.1), and various dioxygenases (EC 1.14.12.x), suggesting an active microbial response to pesticide-induced stress. Overall, sub-lethal TFM exposure disrupts the gut-microbiota axis and metabolic health of L. rohita. These findings emphasize the ecological risks of agricultural runoff in aquaculture and highlight the potential of gut microbes as biomarkers for pesticide-mediated toxicity and detoxification.