Residues of oxolinic acid and oxytetracycline in fish and sediments from fish farms

The residues of oxolinic acid and oxytetracycline were studied in fish and sediments from five fish farms after chemotherapy of the farmed fish. Compared to oxytetracycline, oxolinic acid was better absorbed and faster excreted from the treated fish. Oxytetracycline was found persistent in concentrations of 0.8–6.3 μg/g in the sediments under the medicated fish pens. Oxolinic acid levels of 0.05–0.2 μg/g were measured in the sediments for 5 days after the treatment of the fish. Compared to oxytetracycline, oxolinic acid showed a faster loss of antibacterial activity in the fish farm sediments. Fish pathogenic bacteria resistant to oxytetracycline were isolated from the treated fish and from the sediments under fish pens. No fish pathogenic bacteria resistant to oxolinic acid were found in this study.