Effects of 17α-ethinylestradiol (EE2) on reproductive endocrine status in mummichog (Fundulus heteroclitus) under differing salinity and temperature conditions

• We exposed adult mummichog to 50 ng/L or 250 ng/L of ethinylestradiol under varying temperature and salinity conditions.
• Changes in salinity had little effect on gonadal steroid production of mummichog.
• Temperature is a significant factor regulating northern mummichog reproduction.
• Increased temperature triggered gonadal growth and maturation in both female and male mummichog.
• EE2 counteracted temperature-related effects in mummichog by attenuating the temperature-induced increases in gonad size in males.

Exposure to 17α-ethinylestradiol (EE2), a synthetic estrogen, has previously been shown to decrease reproductive endocrine status and egg production in northern mummichog (Fundulus heteroclitus macrolepidotus). The objective of this study was to evaluate if variations in salinity or temperature conditions of EE2-exposed mummichog modify the effect on whole organism reproductive endocrine status and gonadal steroidogenesis. Mummichog were exposed in vivo for 14 days to 0, 50 and 250 ng/L EE2 in 0, 16 and 32 ppt salinity at 18 °C and to 0 and 250 ng/L EE2 at 10, 18 and 26 °C at 16 ppt. There was a little overall effect of salinity on measured endpoints. In the salinity exposure, 250 ng/L EE2-exposed females had significantly reduced 17β-estradiol (E2) levels. Increased temperature triggered gonadal growth in both sexes and increased plasma E2 and E2 production and decreased 11-KT (11-ketotestosterone) production. EE2 counteracted the effect of temperature by depressing gonadal growth in males. In both exposures, EE2 effects on testosterone (T) production were variable. The use of steroidogenic precursors (25-OH-cholesterol, and/or pregnenolone and/or testosterone) in the in vitro gonadal incubations indicated decreased E2 production in females and 11-KT production in males were predominately due to suppression of the terminal conversion step between T and E2 or 11-KT. Ovarian aromatase A (cyp19a) gene expression at 16 ppt and 18 °C was not affected by 250 ng/L EE2 (the only treatment combinations tested). Overall, temperature is a factor regulating northern mummichog reproduction; EE2 overrides its effects and disrupts the terminal step of steroidogenesis. Our results should be considered in designing future estuarine fish bioassays and in understanding effects of estrogenic endocrine disruptors in estuaries.