Effects of exposure water volume, depuration time, and feeding status on vitellogenin mRNA induction in male medaka (Oryzias latipes) exposed to17 β-estradiol

Bioassays measuring the induction of vitellogenin gene expression in male fish are widely used for revealing estrogenic activity in water samples. Measuring induction of vitellogenin mRNA in males by means of RT-PCR analysis is a sensitive way to detect exposure to estrogenic chemicals. To date, little work has been done to examine variations in exposure conditions for assessing estrogenic activity in water samples using this model system. Here we report the results of experiments investigating the effects of volume of treatment water, time since removal from treatment water (depuration), and short-term food deprivation on vitellogenin mRNA induction in male Japanese medaka (Oryzias latipes). Fish exposed to a single concentration of E2 while volume was manipulated were found to have similar levels of vitellogenin mRNA, though more E2 was present at larger volumes. Removal of fish from E2-treated-water to clean water after exposures reduced vitellogenin levels in as little 24 h, however, the vitellogenin levels of the fish transferred to the clean water remained above those of the control fish for at least 72 h. Depriving fish of food for up to 72 h during exposure to E2 did not significantly reduce vitellogenin induction. Together these results support the conclusion that real time RT-PCR measurement of vitellogenin in male fish can be used as a robust indicator of exposure to estrogenic contaminants in water.