Laboratory and field-caging studies on hepatic enzymatic activities in European eel and rainbow trout.

Caging field experiments were conducted on young European eel (Anguilla anguilla) and on rainbow trout (Onchorynchus mykiss) for the determination of a biomonitoring protocol of freshwater streams. Hepatic monooxygenase and conjugation enzyme activities were measured as biomarkers of exposure to some organic pollutants. Laboratory studies were performed to compare the responsiveness of these two species concerning their enzymatic activities. The induction of monooxygenase activity, measured as the deethylation of 7-ethoxyresorufin (EROD activity) was examined by beta-naphtoflavone (beta-NF) treatment. Dose-response study revealed that EROD activity increased significantly from 1 mg beta-NF/kg 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 observed. During a time-course study, EROD activity increased, starting from the second day for both species. In European eel, this enzymatic activity decreased significantly from the seventh day, whereas no significant decrease was observed for rainbow trout after 14 days. During a 2-week field study, EROD and GST activities were measured in fish held in cages upstream and downstream of a polluted area. For both species, the induction of EROD activity was observed in the polluted site after 14 days of caging; GST activity was not significantly affected. Monooxygenase activity appeared to be a sensitive tool for biomonitoring freshwater streams for both species.