In the framework of monitoring programmes organized
under several sea protection conventions (HELSINKI Conv.,
OSPAR Conv.) the contracting parties are requested to
develop appropriate techniques for Biological-Effect-
Monitoring. In following these recommendations the Institut
for Fisheries Ecology studies the 7-ethoxyresorufin-
O-deethylase (EROD) activity in the liver of dab. EROD
represents one enzyme of the cytochrome P-450 species,
also called mixed function oxygenases (MFO), which is
induced by certain organic contaminants, e.g. PCBs. On
the other hand, an influence of natural factors like season,
temperature or spawning on the EROD activity may be
possible. The present study represents an insight into the
status of the EROD activity in North Sea dab. Ultimately,
we intend to decide if EROD activity is an appropriate tool
to detect effects of contaminants. The EROD activity in the
liver of 687 dabs, caught in the North Sea at different seasons in 1995 and 1996 with the fishery research vessel “Walther Herwig III”, has been determined and the data obtained have been statistically evaluated. The logarithmically transformed values of the EROD activity are following approximately a normal distribution. Due to the wide variation of the enzyme activities and due to the small
number of samples minor differences between samples are
not detectable. Nevertheless, comparing the enzyme
activities at different sites of the North Sea, some significant differences have been identified. A model for the discription of seasonal variations of EROD activity, developed at the Biologische Anstalt Helgoland, could be helpful for interpretation
