Environmental pollution caused elevated concentrations of oestradiol and vitellogenin in the female flounder, Platichthys flesus (L.)

Abstract

Female and male flounder, Platichthys flesus, were exposed to various concentrations of polluted harbour dredged spoil in large mesocosms for up to 3 years. The dredged spoil contained a mixture of contaminants representative of pollution concentrations found in the natural environment. Ovarian development, vitellogenesis and steroid hormones in the fish were studied and compared with results from feral fish sampled at a relatively clean field site in the Dutch Wadden Sea. Plasma concentrations of vitellogenin (VTG), established by densitometry in sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) gels, fluctuated during the annual reproductive cycle of the Wadden Sea flounder and reached a maximum during autumn and winter (advanced vitellogenesis). Fish held in the polluted mesocosm for 3 years exhibited premature vitellogenesis, resulting in a high number of oocytes in the yolk granule stage in spring, normally the previtellogenic period of the year. Moreover, VTG was significantly elevated in the plasma of these females relative to the concentrations in fish from the reference mesocosm. The high concentration of plasma VTG in females from the polluted mesocosm coincided with significantly elevated concentrations of testosterone and 17β-oestradiol. The in vitro ovarian production capacity of these steroids, however, was not altered. In feral and pollution-exposed male flounder, no VTG was detected. On the basis of these findings, it was concluded that premature vitellogenesis in the female flounder was a result of elevated 17β-oestradiol concentrations rather than a direct endocrine effect of xeno-oestrogenic contaminants. It is suggested that the elevated 17β-oestradiol concentrations are caused by decreased clearance rates of steroids in the blood.