Mummichog (Fundulus heteroclitus) are less sensitive to 17α-ethinylestradiol (EE) than other common model teleosts: A comparative review of reproductive effects.

The environmental estrogen 17α-ethinylestradiol (EE) will depress or completely inhibit egg production in many common model teleosts at low concentrations (≤0.5 ng/L; Runnalls et al., 2015). This inhibition is not seen in the estuarine killifish, or mummichog (Fundulus heteroclitus), even when exposed to 100 ng/L EE. This relative insensitivity to EE exposure indicates species-specific mechanisms for compensating for exogenous estrogenic exposure. This review compares various reproductive responses elicited by EE in mummichog to other common model teleosts, such as zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), identifying key endpoints where mummichog differ from other studied fish. For example, EE accumulates primarily in the liver/gall bladder of mummichog, which is different than zebrafish and fathead minnow in which accumulation is predominantly in the carcass. Despite causing species-specific differences in fecundity, EE has been shown to consistently induce hepatic vitellogenin in males and cause feminization/sex reversal during gonadal differentiation in larval mummichog, similar to other species. In addition, while gonadal steroidogenesis and plasma steroid levels respond to exogenous EE it is generally at higher concentrations than observed in other species. In mummichog, production of 17β-estradiol (E) by full grown ovarian follicles remains high; unlike other teleost models where E synthesis decreases as 17α,20β-dihydroxy-4-prenen-3-on levels increase to induce oocyte maturation. New evidence in mummichog indicates some dissimilarity in gonadal steroidogenic gene expression responses compared to gene expression responses in zebrafish and fathead minnow exposed to EE. The role of ovarian physiology continues to warrant investigation regarding the tolerance of mummichog to exogenous EE exposure. Here we present a comprehensive review, highlighting key biological differences in response to EE exposure between mummichog and other commonly used model teleosts.