Residues of oxolinic acid in wild fauna following medication in fish farms

Abstract

Dispersion of oxolinic acid and occurrence of Aeromonas salmonicida in wild fauna were studied in animals captured in the vicinity of 2 aquaculature facilities during and after medication with this drug. Consumption of antibacterial agents in aquaculture has reached a considerable level. The major part of the drugs used reach the environment, either directly due to excessive feeding and reduced appetite of the cultured fish, or indirectly after having passed through the fish. Some of the drugs entering the environment are taken up by exploitable wild fish, shellfish, and crustaceans, resulting in concentrations far above those accepted in food for human consumption in Norway. The concentration of oxolinic acid in muscle and liver was highest in pelagic fish like coalfish and mackerel. The mean concentration in muscle of all positive samples at the day of medication termination were 4.38 .mu.g g-1 and 0.42 .mu.g g-1 at 2 different farms. Maximum concentration of oxolinic acid in muscle samples was 12.51 .mu.g g-1. We found a simultaneous occurrence of oxolinic acid and the fish pathogenic bacterium A. salmonicida in the gut of both cultured and wild fish. This may lead to development and dispersion of resistant bacteria. Blue mussels Mytilus edulis harvested at one of the farms contained an elevated level of bacteria resistant to oxolinic acid.