Effects of 17α-ethynylestradiol on early-life development, sex differentiation and vitellogenin induction in mummichog (Fundulus heteroclitus)

Fertilized mummichog eggs retrieved from 17α-ethynylestradiol (EE2) exposed adult fish were raised in concentrations of EE2 ranging from 0 to 100 ng/L (100 ng/L EE2 estimated to have actual average exposure concentrations of 30% of nominal; 0.1–10 ng/L were below detect throughout 24-h exposure period) for 61 weeks post-hatch. Eggs exposed at 100 ng/L hatched sooner, the larvae were longer, and survival of juvenile fish from hatch to study termination was greater than all other treatments, though fewer hatched at this treatment. Sex ratios were skewed (>80% female phenotype) at 100 ng/L EE2, and some gonadal male fish displayed female secondary sex characteristics. Condition factor, gonadosomatic index (GSI), and liver somatic index (LSI) were found to decrease in both sexes between 52 and 61 weeks post-hatch. Female fish had increased hepatic vitellogenin (VTG) at 52 weeks post-hatch. When exposed to 1, 10 and 100 ng/L EE2, female fish had a higher proportion of vitellogenic follicles in the ovarian tissue. Males exposed at 100 ng/L may have had disruption at some endpoints (GSI, VTG) that is masked due to reduced sample size compared to other treatments. Fish exposed to concentrations of EE2 at or below 10 ng/L showed inconsistent effects on development and reproductive potential. This study indicates the potential for population-level effects at the high range of environmental EE2 at concentrations equivalent to those at which consistent effects in fecundity in the adult mummichog reproductive test have been measured. This work demonstrates that chronic EE2 exposure causes developmental effects at concentrations similar to those which cause effects in the shorter-term adult mummichog reproductive test. Effects are at higher concentrations than have been noted for freshwater model species. Whether this is because of species sensitivity or due to differences between freshwater and saltwater availability of EE2 or its uptake requires further study.