2026 Volume 61 Issue 2 Pages 64-67
Minimum inhibitory concentrations (MICs) of nine antibacterial agents were determined for Mycobacterium paragordonae pathogenic to koi carp Cyprinus carpio. MICs of ampicillin and florfenicol against 10 isolates were in the range of < 0.06–0.25 and < 0.06–0.5 μg/mL, respectively. Ampicillin (20 mg/kg/day) and florfenicol (10 mg/kg/day) were orally administered to koi carp challenged with M. paragordonae for 5 days (FF-5 and ABPC-5) or two 5-day periods separated by a 10-day withdrawal period (FF-10 and ABPC-10). Cumulative survival rates in florfenicol-treated groups were significantly higher than those in the control group, whereas those in the ampicillin-treated groups were not. Oral administration of florfenicol is a promising countermeasure against M. paragordonae in koi carp.
