Florfenicol residues in three species of fish after 10-day oral dosing in feed.

Nile tilapia Oreochromis niloticus, walleye Sander vitreus, and hybrid striped bass (female white bass Morone chrysops x male striped bass M. saxatilis) were medicated with florfenicol (AQUAFLOR type A medicated article; Schering-Plough Animal Health, Summit, New Jersey) via a medicated ration of 10 mg florfenicol x kg fish body weight(-1) d(-1) for 10 d to compare the elimination kinetics of the test article. This study was part of a larger effort in support of a species grouping concept that could contribute to the regulatory approval process for therapeutic compounds for cultured fishes. The trials in this study were conducted at the ideal water temperature for each species and at the temperature 5 degrees C lower than the ideal. The test temperatures were 30 degrees C and 25 degrees C for Nile tilapia, 25 degrees C and 20 degrees C for both walleyes and hybrid striped bass. In all cases, the elimination kinetics of florfenicol were more rapid at higher temperatures. The time to reach the tolerance of 1 microg/g in muscle-skin, as set by the U.S. Food and Drug Administration for channel catfish Ictalurus punctatus and salmonids, ranged from 6.1 to 4.1 d for Nile tilapia, from 12.6 to 9.7 d for walleyes, and from 2.6 to 0.7 d for hybrid striped bass at temperatures between 20 degrees C and 30 degrees C.