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

Dispersion of oxolinic acid and occurrence of Aeromonas salmonicida in wild fauna were studied in animals captured in the vicinity of 2 aquaculture 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

Presence of the fish pathogen Vibrio salmonicida in fish farm sediments.

The persistence of the fish pathogen Vibrio salmonicida in fish farm sediments was studied by use of fluorescent-antibody techniques. The specificities of the monoclonal antibodies and polyclonal rabbit serum used in the study were tested against a number of Vibrio strains, including 4 isolates from intestinal tracts of healthy fish and 98 isolates from sediments. V. salmonicida was detected in sediment samples from diseased farms several months after an outbreak of the disease. The bacterium was also detected in a sediment sample from a disease-free fish farm. No V. salmonicida could be detected in sediments not influenced by fish farming. The number of positive samples was generally higher with application of rabbit serum as opposed to use of monoclonal antibodies, indicating that the rabbit serum may cross-react with other bacteria