Temporal variation of CYP1A indices, PCB and 1-OH pyrene concentration in flounder, Platichthys flesus, from the Dutch Wadden Sea

Two surveys were carried out to examine the temporal variation of hepatic cytochrome P450 IA (CYPIA) indices and indices of exposure to organic contaminants in flounder, Platichthys flesus, in the Dutch Wadden Sea. Hepatic CYPIA protein was measured immunochemically using a semiquantitative ELISA, and also by its catalytic activity using the 7-ethoxyresorufin O-deethylation activity (EROD) assay. Concentrations of a selection of CB congeners in muscle and liver, and concentrations of 1-OH pyrene in bile, were used as indicators of exposure to PCBs and PAHs respectively. Both classes of compounds contain CYPIA-inducing congeners. Muscle and liver concentrations of CB congeners remained stable between June and March. However, a distinct peak in concentrations occurred just after the spawning period during March to April, but only in mature males. This peak could be associated with the presence of a population of migrating fish at the sampling location at that particular time. The concentration of 1-OH pyrene in bile showed a very different temporal pattern, with lowest concentrations just after the spawning period. CYPIA indices remained stable from June to October, but a distinct peak occurred immediately after the spawning period. In adult flounder, sex-related differences in EROD activity were observed during the spawning period, and sex-related differences in CYPIA protein level during the post-spawning period (March to June). The results of the present study indicate that spawning-related seasonal fluctuations in CYPIA indices and PCB concentrations in flounder are comparable to those observed in other fish species. Monitoring programmes incorporating the measurement of these parameters should take seasonal fluctuations into account. Such programmes should preferably focus on the period June to October in order to minimise the influence of physiological processes and migratory behaviour associated with the annual reproductive cycle. If this is done, sampling does not need to take into account the sex, sexual maturity, or morphological state of the fish, although limiting the range of lengths incorporated in the sample to, say, 18 to 32 cm, will avoid excessive variation in fish age.