INFLUENCE OF OXYTETRACYCLINE AND OXOLINIC ACID ON THE IMMUNE-RESPONSEOF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Oxytetracycline and oxolinic acid were tested for possible immunomodul atory effects on fish. The aim of the study was to follow the kinetics of the immune response after vaccination with simultaneous antibiotic treatment. The fish were immunised with a commercial oil-based divale nt (furunculosis/vibriosis) vaccine and were simultaneously given oral antibiotic treatment. The specific immune response was monitored by a nalysing the levels of specific antibodies with ELISA. As an indicator of the nonspecific immune response, the phagocytic activity of circul ating leucocytes was measured by a chemiluminescence assay. Total circ ulating leucocyte counts and differentials were also monitored. The di sease resistance was evaluated by challenge tests at the end of the ex periment. The results indicate that both oxytetracycline and oxolinic acid significantly suppress antibody production as well as the level o f circulating white cells, especially lymphocytes, in rainbow trout wh en administered in association with immunisation. The phagocytic activ ity of whole blood leucocytes was stimulated by oxolinic acid and slig htly suppressed by oxytetracycline. The survival after challenge was n ot significantly affected by the antibiotics in the present tests. (C) 1998 Academic Press Limited.