LABORATORY AND FIELD-CAGING STUDIES ON HEPATIC ENZYMATIC-ACTIVITIES IN EUROPEAN EEL AND RAINBOW-TROUT

Caging field experiments were conducted on young European eel (Anguill a anguilla) and on rainbow trout (Onchorynchus mykiss) for the determi nation of a biomonitoring protocol of freshwater streams. Hepatic mono oxygenase and conjugation enzyme activities were measured as biomarker s of exposure to some organic pollutants. Laboratory studies were perf ormed to compare the responsiveness of these two species concerning th eir enzymatic activities. The induction of monooxygenase activity, mea sured as the deethylation of 7-ethoxyresorufin (EROD activity) was exa mined by beta-naphtoflavone (beta-NF) treatment. Dose-response study r evealed that EROD activity increased significantly from 1 mg beta-NF/k g bw and was on a plateau at 50 mg beta-NF/kg bw for both species. No significant effect on glutathione S-transferase (GST) activity was obs erved. During a time-course study, EROD activity increased, starting f rom the second day for both species. In European eel, this enzymatic a ctivity decreased significantly from the seventh day, whereas no signi ficant decrease was observed for rainbow trout after 14 days. During a 2-week field study, EROD and GST activities were measured in fish hel d in cages upstream and downstream of a polluted area. For both specie s, the induction of EROD activity was observed in the polluted site af ter 14 days of caging; GST activity was not significantly affected. Mo nooxygenase activity appeared to be a sensitive tool for biomonitoring freshwater streams for both species. (C) 1998 Academic Press.