EFFECTS OF THE ANTIBIOTIC BAYTRIL (ENROFLOXACIN) ON PCB-INITIATED INDUCTION OF CYTOCHROME P4501A MESSENGER-RNA IN SEXUALLY MATURE ATLANTIC TOMCOD (MICROGADUS TOMCOD)

We used a factorial experimental design to determine whether the antim icrobial Baytril (enrofloxacin) had an effect on induction of cytochro me P4501A (CYP1A) mRNA in Atlantic tomcod. Fish were injected with cor n oil, Baytril and corn oil, Baytril and 3,3',4,4'-tetrachlorobiphenyl (PCB) dissolved in corn oil, or just PCB in corn oil. Analysis of gen e induction in both sexes considered together showed significant induc tion by PCB treatment and a significant effect of sex (males higher th an females). Because the experiment was carried out just before spawni ng, our results provide additional evidence for pretranslational suppr ession of CYP1A induction in spawning females. Separate analysis of th e sexes showed that in both males and females, PCB had a significant e ffect on induction. However, in analyzing the males we also observed s ignificant induction by Baytril alone. In addition, the BaytrilPCB com bination resulted in the highest induction in any group. These finding s demonstrate the potential for confounding results due to exposure of sampled fish to antibiotics, either in a laboratory or field situatio n.