Gut microbiome profiling of antibiotic-treated Mystus cavasius using culture-based and shotgun metagenomic approaches

Antibiotic use in aquaculture prevents disease and promotes growth but can disrupt the gut microbiome and drive resistance. The study profiled the gut microbiome of antibiotic-treated Mystus cavasius using both culture-based and shotgun metagenomic approach. Culture-dependent analysis revealed a significant 2-threefold reduction in total viable bacterial count in treated fish. Phylogenetic analysis of 12 cultured isolates revealed treatment-driven enrichment of Bacillus, Enterobacter and Aeromonas. Antibiotic susceptibility testing further revealed increased resistance profiles among isolates from treated fish. Metagenomic profiling identified over 1400 bacterial species and revealed clear taxonomic shifts. Control groups were enriched with beneficial genera such as Lactiplantibacillus and Arthrospira, while treated fish were dominated by opportunistic or resistant taxa including Plesiomonas, Staphylococcus, and Acinetobacter. These shifts were further reflected at the phylum level, with a decline in Proteobacteria and Bacteroidetes, accompanied by an increase in Firmicutes and the enrichment of antibiotic-tolerant lineages. Treated samples exhibited more uniform alpha diversity indices, suggesting a restructuring of the microbial community hierarchy following oxytetracycline exposure, whereas beta diversity analysis showed a moderate separation between control and treated groups. These findings provide critical insights into the ecological and health risks of antibiotic use in aquaculture and underscore the importance of developing sustainable alternatives for disease management in fish farming.