Screening estrogenic activity of environmental contaminants and water samples using a transgenic medaka embryo bioassay

► First study to directly investigate the effects of xenoestrogens on GnRH neurons. ► Used a novel transgenic medaka embryo bioassay. ► The embryos are transparent, rendering in vivo observation possible. ► The fluorescence and other endpoints used are easily quantifiable. ► The embryos are sensitive to estrogenic action of environmental contaminants.