XENOBIOTIC METABOLIZING ENZYMES IN UNINDUCED AND INDUCED RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) - EFFECTS OF DIETS AND FOOD-DEPRIVATION

1. Untreated and beta-naphtoflavone (BNF)-treated trout (Oncorhynchus mykiss) were maintained for 15-21 days under 3 different feeding regimens or under starvation. 2. Possible diet effects were studied by measuring the following 13 hepatic parameters: aminopyrine demethylase (APDM), ethoxyresorufin-O-deethylase (EROD), benzo(a)pyrene hydroxylase (AHH), UDP glucuronyltransferase (UDPGT), glutathione reductase (GR), glutathione-S-transferase (GST), glutathione peroxidase (GPx), glucose 6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) enzyme activities; the content of total cytochrome P-450 (P-450); proteic and non-proteic SH groups (SHP, SHNP) and liver somatic index (LSI). 3. The results show that some feeding regimens affect a large number of these parameters in both uninduced and BNF-treated fish. 4. Hence, caution should be imposed in the use of the biochemical markers as a water-quality monitoring tool. 5. In particular, it is advisable to maintain fish without feeding during short-term experiments, especially because trout exhibit an excellent biochemical response to inducer even after a 21-day starvation period. 6. Conversely, when fish are to be necessarily fed (long-term experiments), diet must be carefully chosen and controlled by preliminary tests because some commercial fish pellets contain both inducers and inhibitors of several microsomal/cytosolic enzymes.