Impact of Long-Term Exposure to 17α-Ethinylestradiol in the Live-Bearing Fish Heterandria formosa

17α-ethinylestradiol (EE2) is a potent synthetic estrogen that is routinely detected in aquatic ecosystems and exhibits estrogenic activity. Acute and chronic toxicity have been described for oviparous and ovoviviparous fish species; however, no information is available on the impacts of EE2 on viviparous, matrotrophic fish despite their ecological importance. The present study investigated the consequences of long-term EE2 exposure in the least killifish (Heterandria formosa). Effects on growth, time-to-sexual maturity, fecundity, and offspring survival were examined in an 8-month, life-cycle experiment. Starting as 0–6-day-old fish, least killifish were continuously exposed to EE2 at nominal concentrations of 0, 5, or 25 ng/L (measured concentrations averaged 0, 4.3, and 21.5 ng/L respectively). In the F0 generation, EE2-exposure did not affect survival but resulted in increased time-to-sexual maturity and a sex-dependent effect on size; female standard length was reduced while male standard length was increased. This caused the ordinarily larger females and smaller males to become more similar in size. Condition factor was reduced for both sexes. Fecundity was reduced by 50% and 75% at 5 and 25 ng/L EE2-exposure respectively. Continued EE2-exposure in the F1 generation resulted in significantly reduced survival. These results suggest that despite their matrotrophic development, these fish experience delayed development and reduced reproductive success from EE2-exposure and that effects appear to intensify in the second generation.