Seasonal variation in ethoxyresorufin O-deethylase (EROD) activity in European eels Anguilla anguilla and flounders Pleuronectes flesus from the Severn Estuary and Bristol Channel

The Severn Estuary and Bristol Channel form the largest estuary in the UK. The estuary receives organic contaminants, including polyaromatic hydrocarb ons (PAHs) and polychlorinated biphenyls (PCBs) from diverse sources. Altho ugh hepatic ethoxyresorufin O-deethylase (EROD) activity has been widely us ed as a biomarker for organic contamination in fish, its activity can be af fected by a number of seasonal and environmental factors. We therefore meas ured EROD activity in the Liver of European eels Anguilla anguilla and flou nders Pleuronectes flesus, 2 abundant species in the Severn Estuary. Fish w ere collected from the water-intake screens of 2 nuclear power stations, lo cated at Oldbury-upon-Severn and Hinkley Point, every 2 to 4 wk between Mar ch 1996 and February 1998. EROD activity in eels showed pronounced seasonal variation. Maximum activity (656 to 820 pmol min(-1) mg(-1) protein) occur red in the warmest summer months and lowest activity (117 to 128 pmol min(- 1) mg(-1) protein) in the coldest winter months. EROD activity was also ele vated during the summer in flounders (470 to 650 pmol min(-1) mg(-1) protei n) but the highest EROD activities (up to 1546 pmol min(-1) mg(-1) protein) occurred in the winter/spring when spawning occurs in this species. Howeve r, these elevations occurred even in immature 1+ and 2+ flounders, suggesti ng that some other physiological/endocrinological cycles relating to day le ngth may also be involved. Intraperitoneal injection of benzo[a]pyrene resu lted in increased EROD activity in both species to levels similar to the ma ximum observed in fish from the field. The results confirm that pronounced variation in EROD activity is associated with season and age in eels and fl ounders and these factors should be considered when employing this biomarke r in the field.