Xenobiotic-metabolizing enzyme systems in test fish. I. Comparative studies of liver microsomal monooxygenases

All monooxygenase activities assayed in guppy (Poecilia reticulata) and red killifish (Oryzias latipes) were 7-10 times higher than those measured in trout (Salmo gairdneri), carp (Cyprinus carpio), and golden orfe (Leuciscus idus). Cytochrome P-450 was 3 times higher in the former fish than in all the other species. Zebra fish (Brachydanio rerio) 7-ethoxycoumarin O-deethylase and bluegill (Lepomis macrochirus) ethylmorphine N-demethylase (EMND) were not greatly different from those of the former group. alpha-Naphthoflavone (NF) and methyrapone (MET) exerted qualitatively different actions on benzo[a]pyrene hydroxylase of guppy, trout, and bluegill liver: both chemicals enhanced the bluegill activity and inhibited that of trout; the guppy liver enzyme was inhibited by MET and activated by NF. EMND activity was inhibited by either compound in the three species. The relevance of all these data to the European Economic Community ecotoxicity tests is discussed.