Seasonal variations in the activities of selected hepatic biotransformation and antioxidant enzymes in eelpout (Zoarces viviparus).

The eelpout (Zoarces viviparus) is used in Swedish and German environmental monitoring of pollutant effects in fish and is being considered for the same purpose in other countries, mainly around the Baltic Sea. The activities of several hepatic biotransformation and antioxidant enzymes were monitored during the period of 12 months from August 1996 to July 1997, using newly caught feral eelpout from Kattegat, off the west coast of Sweden. In females, the biotransformation enzyme activities showed significant seasonal variations, although the amplitude of the changes was limited; CYP1A-activity, measured as ethoxyresorufin-O-deethylase (EROD), was highest in February-March and decreased afterwards, possibly due to rising estrogen levels. UDP-glucuronosyltransferase activity was lowest in November, while the glutathione-S-transferase activity markedly decreased during the winter. The antioxidant enzymes, catalase, glutathione peroxidase and glutathione reductase showed small variations in their activity. The number of male fish was limited and the seasonal variations less clear. However, in both sexes, glutathione reductase and peroxidase activities were highest in autumn and May, respectively. This study establishes a baseline for the activities of the selected enzymes in female eelpout, which is important for the environmental monitoring using this fish species.