USE OF ENROFLOXACIN TO CONTROL ATYPICAL AEROMONAS-SALMONICIDA IN ATLANTIC TOMCOD

The antimicrobial enrofloxacin was tested for its ability to control a typical Aeromonas salmonicida in Atlantic tomcod (Microgadus tomcod). An initial experiment showed that a single injection of enrofloxacin, at a dosage of approximately 5 mg active ingredient per kilogram of fi sh, prevented the formation of characteristic furunculosis lesions but did not significantly reduce mortality during a 76-d period. In a sec ond experiment, in which we administered the antimicrobial at days 1, 10, and 45, treated fish experienced significantly lower mortality tha n did the control fish. Three of 10 necropsied fish treated with enrof loxacin produced positive cultures of atypical A. salmonicida, whereas the pathogen was successfully cultured from 7 of 10 control fish. Cul tures were obtained from skin lesions or from infected areas of buccal or caudal regions. Sixteen of 50 (32%) fish from the enrofloxacin tre atment died during the experiment, and 30% of the dead fish displayed circular lesions on the trunk. In the control group, 48 of 50 fish (96 %) died during the experiment, and 78% of the dead fish had lesions on the trunk. In both treatment and control groups, dead fish without le sions on the trunk had either badly eroded tails or infected mouths. W e feel that enrofloxacin holds promise for short-term control of atypi cal A. salmonicida in nonsalmonids.