Catfish is one of the leading finfish species produced in the United States, with Mississippi and Alabama being the two major producing states. Unfortunately, bacterial infections have been a persistent concern for catfish farmers, and antibiotics are often prescribed to control these infections. Bacterial infections in catfish are largely dependent on water temperature. The U.S. Food and Drug Administration (FDA) has approved three antibiotics for use in catfish via medicated feeds: florfenicol, sulfadimethoxine/ormetoprim, and oxytetracycline dihydrate. While these drugs are used solely for treating infections, the formation of antimicrobial-resistant bacteria (ARB) and the potential for horizontal transfer of antimicrobial resistance (AMR) genes remain major concerns. However, the effects of water temperature at the time of antibiotic application on AMR dynamics in rearing water and in the fish gut remain largely uninvestigated. This project aims to bridge this knowledge gap by conducting live-fish trials.
The three FDA-approved drugs were applied to catfish fingerlings at three temperatures (20, 25, and 30 °C). Shotgun metagenomic analyses were conducted on rearing water and catfish gut samples collected before treatment, after treatment, and after the withdrawal period. Results revealed a U-shaped temperature response was observed in the water microbiome for florfenicol- and Romet-associated ARG shifts, with the smallest change at 25 °C. Although tetracycline treatment also had the smallest impact on ARG abundance and diversity at 25 °C, the abundance of tetG continuously increased as the temperature increased. Results from the intestinal microbiome sequencing also proved strong temperature-dependent AMR dynamics, with the least change of AMR observed at 20 °C, whereas 25 °C and 30 °C leading to broader shifts in community composition and resistance gene profiles. This study demonstrates that water temperature interacts with different antibiotics to significantly influence AMR development in both rearing water and the intestinal microbiome of catfish. Understanding these dynamics is essential for guiding the prudent use of antibiotics in aquaculture.