SEASONAL-VARIATION OF HEPATIC EROD ACTIVITY IN FLOUNDER (PLATICHTHYS-FLESUS) IN THE DUTCH-WADDEN-SEA

The use of hepatic 7-ethoxyresorufin O-deethylase (EROD) activity in f lounder (Platichthys flesus) as a potential biomarker of marine pollut ion by organic chemicals (as indicated by hepatic PCB-153 concentratio n) was investigated in the Dutch Wadden Sea in 1989 and 1990. Particul ar attention was paid to the seasonal variation. The results indicate that EROD activity was reasonably stable during the year, except for a period in January-February when a marked peak occurred. This peak coi ncided with the absence of mature flounder from the sampling area prob ably due to the spawning migration. Generally a good relationship exis ted between hepatic EROD activity and PCB-153 concentration, with one exception. During the period January-April 1990 a peak in PCB-153 conc entration occurred immediately after the observed peak in EROD activit y. It is concluded that the best period for monitoring EROD activity i n flounder is the summer, corresponding to the non-migratory period of the species.