In vivo and in vitro effect of oxytetracycline treatment on the immune response of turbot, Scophthalmus maximus (L.)

Oxytetracycline (OTC) is one of the most frequently used antibiotics in aqu aculture, although negative side-effects have been reported in some cases. The present study has determined the effect of the in vivo administration o f OTC on several immune functions in turbot, Scophthalmus maximus (L.), suc h as kidney macrophage respiratory burst, phagocytosis and plasma bacterici dal activity. Total plasma protein was also measured. The antibiotic was ad ministered orally over 12 days, and this treatment was combined with OTC ba ths on days 1, 3 and 5. The drug did not suppress the immune functions anal ysed. Instead, the treatment produced a significant increase in the plasma bactericidal activity and total protein concentration. The effect of differ ent doses of OTC on macrophage functions (i.e. respiratory burst activity a nd phagocytosis) and cell viability was also assayed in vitro. Although cel l viability did not decrease after in vitro exposure, head kidney macrophag e respiratory burst and phagocytosis were inhibited by the in vitro treatme nt, and were dose-dependent.