Evaluation of the efficacy of enrofloxacin in rainbow trout (Oncorhynchus mykiss) following experimental challenge with Yersinia ruckeri.

BACKGROUND Use of enrofloxacin in trout farms is reported, especially for the treatment of yersiniosis, albeit various dosing regimens have been used. Therefore, optimal doses should be investigated. METHODS Five groups of 15 fish were challenged with Y. ruckeri. Two days later, three groups received feed containing enrofloxacin (ENR) at 1, 2.5 and 5 mg/kg fish respectively, during 7 days; one group received a single intraperitoneal injection of ENR at 10 mg/kg; and one group was left untreated. On day 15, surviving fish were euthanized. RESULTS All fish survived in the group treated by injection, compared to 53%, 60% and 40% of the fish treated with 1, 2.5 and 5 mg/kg oral ENR, respectively, and 53% in the infected untreated group. CONCLUSION A single intraperitoneal injection of ENR at 10 mg/kg seems more relevant than repeated oral administrations. The ENR oral doses used in trout farms should be revised.