Juvenile rainbow darters (Etheostoma caeruleum) were exposed to nominal concentrations of 20 to 1,000 ng/L of 17alpha-ethynylestradiol (EE2) at 120 d posthatch and in a subsequent experiment to 200 ng/L of EE2 with 2.0 to 20,000 ng/L of tamoxifen (TMX) at 150 d posthatch to determine the threshold of estrogen-induced morphological and histological changes in a sexually dimorphic benthic fish species ecologically relevant to southern Minnesota (USA). 17Alpha-ethynylestradiol induced female-associated urogenital papillae in males at 200 ng/L, enlargement and development of fibrosis in male testes, enlargement of ovary and oocyte size in females, and large fatty inclusions in the liver of both sexes.
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