Effects on reproductive potential and endocrine status in the mummichog (Fundulus heteroclitus) after exposure to 17α-ethynylestradiol in a short-term reproductive bioassay

A short-term reproductive bioassay with the mummichog (Fundulus heteroclitus) was developed to link changes in endocrine status to reproductive potential subsequent to endocrine disrupting substance (EDS) exposure. Sexually mature mummichog were separated by sex and exposed to the synthetic estrogen 17α-ethynylestradiol (EE2) at nominal concentrations of 0–100 ng/L for 21 days using a static daily renewal protocol. Half of the fish were sampled on Day 21. At 100 ng/L, male fish had induction of vitellogenin (VTG), increased gonadosomatic index (GSI), decreased testosterone production and decreased circulating 11-ketotestosterone (11-KT). Female fish had decreased circulating estradiol (E2) and testosterone (T) at 100 ng/L. There were some impacts at lower concentrations of EE2 in both sexes, though the results were not consistent. On Day 21, the remaining male and female fish were combined at each treatment and exposed for an additional 7 days during which spawning and fertilization success were also assessed. Males exposed to 100 ng/L EE2 exhibited VTG induction, increased GSI, and decreased T production on Day 28. Female fish had increased E2 and T production at 1 and/or 10 ng/L and circulating E2 levels remained depressed above 10 ng/L. Female fish exposed to 100 ng/L spawned fewer eggs; fertilization was also impaired. In a parallel exposure, measured EE2 water concentrations were approximately 10–20% of nominal for the 100 ng/L EE2 treatment over a 24-h static exposure; levels in the other treatments were below detectable levels. Fish exposed to nominal concentrations of EE2 below environmentally relevant levels (i.e., <10 ng/L) showed minimal effects while both the endocrine system and reproductive potential were affected at 100 ng/L EE2 (nominal).