Comparative responsiveness to natural and synthetic estrogens of fish species commonly used in the laboratory and field monitoring

Exposure to estrogenic chemicals discharged into the aquatic environment has been shown to induce feminization in wild freshwater fish and although fish species have been reported to differ in their susceptibility for these effects, empirical studies that directly address this hypothesis are lacking. In this study, in vitro ER alpha activation assays were applied in a range of fish species used widely in chemical testing (including, zebrafish, fathead minnow, medaka) and/or as environmental monitoring species (including, roach, stickleback, carp) to assess their comparative responsiveness to natural (estrone, estradiol, estriol) and synthetic (17 alpha-ethinylestradiol (EE2), diethylstilbestrol (DES)) estrogens. In vivo exposures to EE2 via the water (nominal 2 and 10 ng/L for 7 days) were also conducted for seven fish species to compare their responsiveness for hepatic vitellogenin (VTG) mRNA induction (an ER mediated response). Of the fish species tested, zebrafish ER alpha was found to be the most responsive and carp and stickleback ER alpha the least responsive to natural steroid estrogens. This was also the case for exposure to EE2 with an ER alpha-mediated response sensitivity order of zebrafish > medaka > roach > fathead minnow > carp > stickleback. For VTG mRNA induction in vivo, the order of species responsiveness was: rainbow trout (not tested in the ER alpha activation assays)> zebrafish > fathead minnow > medaka > roach > stickleback > carp. Overall, the responses to steroid estrogens in vitro via ER alpha compared well with those seen in vivo (VTG induction for exposure to EE2) showing in vitro screening of chemicals using fish ER alpha-mediated responses indicative of estrogenic responses (VTG induction) in vivo. (C) 2011 Elsevier B.V. All rights reserved.