Short-term feeding of dietary florfenicol influences gut microbiome and growth performance of fast-growing Silurus meridionalis

Abstract

Florfenicol is a broad-spectrum antibiotic commonly used in aquaculture to control bacterial infections in fish. However, it may induce perturbation on the gut microbiota, compromising growth and fitness. This study aimed to evaluate the gut microbial community, histological alterations, and growth performance of fast-growing southern catfish Silurus meridionalis larvae fed florfenicol-medicated feed (florfenicol group) at 20 mg/kg biomass per day for 7 days as well as the recovery effects for another 7 days by comparing those of the counterparts fed non-medicated feed (control group). The results showed that dietary florfenicol strikingly affected gut microbial community development and caused community perturbation at day 7, with Proteobacteria enrichment up to 99.3% in the florfenicol group and progressive reductions in microbial diversity and evenness. The antibiotic also rapidly led to enrichments of potential opportunistic pathogens such as Citrobacter, Plesiomonas, and unclassified Aeromonadaceae, which may carry more abundant antibiotic-resistance genes. However, the perturbation effects disappeared gradually after dietary florfenicol withdrawal. Metagenomic predictions revealed an increase in the number of altered microbial functions during the administration of dietary florfenicol and a successive decrease after the withdrawal. Dietary florfenicol had no effect on the gut histological structures and mortalities of southern catfish, but it significantly decreased feed intake. The changes in temporally observed community and function coincided with the commencement of decreased feed intake and increased feed conversion ratio in the florfenicol group, consequent to retarded growth during the dietary administration. These alterations were gradually restorable after the dietary florfenicol withdrawal. This study suggests that short-term feeding of dietary florfenicol disturbs the gut microbiota, potentially impairing fish feeding and feed utilization and, lastly, fish growth performance. The results highlight the importance of responsible and prudent use of florfenicol in aquaculture and the need for more studies to understand the health consequences associated with gut microbiome disturbance resulting from antibiotic use in aquatic animals.