Preliminary Assessment of the Tolerance and Efficacy of Florfenicol against Edwardsiella ictaluri Administered in Feed to Channel Catfish

A tolerance study was conducted to determine the palatability of florfenicol to channel catfish Ictalurus punctatus. Four tanks of fish (20 fish/tank) were assigned to each of five treatments distinguished by the amount of florfenicol given in feed per kilogram of body weight, namely, 0,10, 20, 40, or 100 mg. Fish were fed at a rate of 2.5% of body weight per day for 10 consecutive days. On day 11, all surviving fish were euthanatized, counted, and weighed as a group. Florfenicol-medicated feed was palatable to fish at doses of 10, 20, 40, and 100 mg for 10 consecutive days.

All 400 fish were necropsied and examined by histopathology, and no treatment-related changes were observed. In a separate exploratory efficacy study, four tanks (20 fish/tank) were assigned to each of the following treatments: (1) not challenged with Edwardsiella ictaluri and fed un-medicated feed, (2) challenged with E. ictaluri and fed unmedicated feed, (3) challenged with E.ictaluri and fed florfenicol at 10 mg per kilogram of body weight, (4) challenged and fed florfenicol at 20 mg/kg, and (5) challenged and fed florfenicol at 40 mg/kg. Treatment was initiated the day after inoculation, and feed was administered by hand for five consecutive days at 2.5% of body weight. The cumulative mortality observed over a 17-d period in treatment groups 1–5 was 2.5, 57.5, 0, 1.25, and 1.25%, respectively. All 400 fish were necropsied and examined by histopa-thology. The results indicate that florfenicol was effective in controlling mortality from enteric septicemia of catfish with no adverse treatment-related tissue changes. Florfenicol was palatable,safe, and efficacious in controlling mortality due to infection by E. ictaluri in channel catfish.