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Three different physiological parameters were assessed to determine their potential for serving as biomarkers to predict abnormally elevated vitellogenin (VTG) production in male and immature flounder. Whereas abnormally elevated mean VTG plasma concentrations clearly distinguished the Mersey and Dee flounder studied, the results showed no significant differences in estrogen receptor binding capacity or binding affinity between the two groups. Hepatocyte proliferation was not found to be a "biomarker of effect" that could specifically be used to assess an increase in VTG-related proliferation. Nevertheless, immunohistochemical staining for proliferating cell nuclear antigen did show a significantly higher proliferative activity in the livers of Mersey flounder than that in Dee flounder. Sperm motility also was not found to be a biomarker of effect linked to an abnormal elevation of VTG plasma concentration. The results (higher sperm quality in terms of motility in Mersey flounder) were unexpected but interesting.

Vitellogenin (VTG) plasma concentrations were measured in flounder (Platicthys flesus L.) caught in two neighbouring UK estuaries between autumn 1997 and summer 2000. As found in previous studies, male and immature female flounder that were caught in the Mersey, but not in the Dee, had abnormally elevated concentrations of VTG in their plasma-evidence of the presence of natural and synthetic estrogens and/or xenoestrogens in the Mersey. The present study reveals a marked seasonal cycle in VTG concentrations in males. In late spring and summer, male flounder in the Mersey have relatively low concentrations of VTG (microg mL(-1) range). However, in mid-winter, mean concentrations were as high as 5 mg mL(-1). There is also evidence that there was a lessening in the degree of estrogenic endocrine disruption between 1996-1997 (the period of the initial studies on the Mersey) and 1998-2000 (the period covered by the present study). Only 0.5% of the fish contained ovotestes (intersex condition).

In respect to the differences found for vitellogenin (VTG) expression in male and immature flounder, general biological aspects and a set of chemical residues in the liver were compared between flounder from the Mersey and Dee estuaries (UK). Except for alpha-HCH, all pollutant chemicals analysed in flounder liver differed highly significantly between Mersey and Dee fish. Overall, the higher liver contaminant concentrations were found in VTG-induced Mersey flounder. The biomarkers studied were not found to indicate significant differences between Mersey and Dee fish. However, when all of the minor differences are taken into consideration, it appears that the slightly lower growth rates after age 2 in Mersey flounder, lower gonadosomatic index in both mature male and female animals, less precise seasonal patterns of condition factor (CF), hepatosomatic index and gonadosomatic index, and lower CF in immature Mersey fish may well be signs of a contaminant-affected Mersey population.