INFLUENCE OF FLUMEQUINE AND OXYTETRACYCLINE ON THE RESISTANCE OF THE EUROPEAN EEL AGAINST THE PARASITIC SWIMBLADDER NEMATODE ANGUILLICOLA-CRASSUS

The effect of the antibacterial drugs flumequine (FQ) and oxytetracycl ine (OTC) on the defence system of the European eel (Anguilla anguilla L., 1758) was investigated using an experimentally induced infection with the parasitic swimbladder nematode Anguillicola crassus. Eight we eks after oral administration of infective larvae, the mean recovery o f the parasites in FQ-treated eels was lower than in non-medicated con trol animals, and significantly lower than in OTC-treated eels. Mean n umbers of peripheral blood granulocytes and B-lymphocytes, as well as the total number of circulating lymphoid cells, showed a significant i ncrease as a result of the infection, while drug treatment merely affe cted the quantity of the lymphoid cells, The difference in protection against the parasite after FQ or OTC administration points to a modula tion of the fish resistance as a result of the drug treatment, The res ults favour a modulation of the cellular rather than the humoral respo nse, as no specific antibodies were found.