Vitellogenin induction by 17β-estradiol and 17α-ethynylestradiol in male Murray rainbowfish (Melanotaenia fluviatilis).

Hepatic vitellogenin (VTG) mRNA and plasma protein assays were developed for the Murray rainbowfish (Melanotaenia fluviatilis), a native freshwater fish species in Australia. Adult male Murray rainbowfish were exposed to 17β-estradiol (E2) or 17α-ethynylestradiol (EE2) at 0, 1, 5, 10, 50, or 100 ng/L in a semistatic system for 7 d. Vitellogenin mRNA was quantified by quantitative polymerase chain reaction, and VTG protein was semiquantified in plasma using an enzyme-linked immunosorbent assay. Water concentrations were quantified by liquid chromatography coupled with tandem mass spectrometry and were on average 110% and 85% nominal concentrations for E2 and EE2, respectively. Vitellogenin transcripts and protein were upregulated in male Murray rainbowfish exposed to either E2 or EE2 in a dose-responsive manner, with calculated 10% effective concentration (EC10) values for E2 of 3.71 ng/L and 11.6 ng/L for VTG mRNA and protein, respectively, and for EE2 of 2.77 ng/L and 8.47 ng/L for VTG mRNA and protein, respectively. Comparisons of these responses with responses of commonly used test species, including zebrafish (Danio rerio), fathead minnow (Pimephales promelas), and Japanese medaka (Oryzias latipes), revealed the Murray rainbowfish to be a sensitive test species for estrogenic effects via the estrogen receptor pathway. The present study suggests that the Murray rainbowfish would be a suitable candidate for future field studies designed for assessing estrogenic effects of effluent discharges in the Australian freshwater environment.