Impact of administering antibacterial agents on wild fish and blue mussels Mytilus edulis in the vicinity of fish farms

Abstract

Using high-performance liquid chromatography, residues of the quinolones oxolinic acid and flumequine have been quantified in muscle of wild fish. The fish were caught 0 or 1 d after terminating medication in the vicinity of 6 fish farms previously employing one of the drugs. The majority of the wild fish (74 to 100 % of the catch at the different farms) contained drug residues in muscle. The mean muscle concentration varied from 0.95 to 4.89 mug g-1 (ppm). Using a standard microbiological method, 60 % of the examined fish were found to contain faecal material displaying antibacterial activity. The occurrence of bacteria resistant to oxolinic acid and oxytetracycline in blue mussels Mytilus edulis and in the intestinal content of fish was also examined. The level of resistant bacteria was higher in samples taken at the farm after medication than in samples collected before medication or from untreated areas.