The sheepshead minnow as an in vivo model for endocrine disruption in marine teleosts: A partial life-cycle test with 17 alpha-ethynylestradiol

The sheepshead minnow (Cyprinodon variegatus Lacepede), an estuarine fish s pecies, was exposed to 17 alpha -ethynyl-estradiol estradiol (EEZ) at nomin al test concentrations of 0.2, 2, 20, 200, 400, 800, 1,600, and 3,200 ng. F ish were exposed for up to 59 d, from subadult stages to sexual maturity, u nder flow-through conditions. The exposure period was followed by an evalua tion of reproductive success and survival of progeny. The reproductive succ ess of exposed sheepshead minnows, as determined from data on egg productio n from two subsequent spawning trials, was reduced in fish exposed to 200 n g[L EE2 and, in one spawning trial, in the 20-ng/L treatment. Hatching succ ess was reduced in the progeny of fish exposed to 200 ng/L EE2, but surviva l was good among fry that successfully hatched. Histological examination in dicated generalized edema, damage to gill epithelia, hepatic toxicity, fibr osis of the testis, and evidence of sex reversal, including testes-ova and spermatagonia-like, cells in ovaries. The maximum acceptable toxicant conce ntration (MATC) for gonadal development in males was within the normal rang e of EE2 concentrations in sewage treatment plant effluents. The exposure r egimen and choice of test organism, combined with histological examination, allowed independent evaluation of ecologically significant acute, reproduc tive and estrogenic endpoints. Estrogen receptor-mediated effects occurred at concentrations where reproductive effects were measurable under standard reproduction assays. The sheepshead minnow appears to be a sensitive in vi vo model for partial life-cycle testing of compounds that have the potentia l to disrupt the endocrine system as well as reproduction in estuarine and coastal marine fish species.