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

The eelpout Zoarces viviparus is used in Sweden for environmental monitoring of pollutant effects in fish. 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 Kattegatt, off the west coast of Sweden. In females, the enzyme activities showed significant seasonal variations; CYP1A-activity, measured as ethoxyresorufin-O-deethylase (EROD), was lowest during the spawning season in August, possibly due to high estrogen levels. UDP-glucuronosyl transferase activity was lowest in November, while the glutathione-S-transferase activity markedly decreased during the winter. On the other hand, catalase activity peaked in April. 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 the autumn and in May, respectively. The results are important for the ability to distinguish between pollutant effects and natural variations in the activity of selected enzymes in eelpout.