Development of a short-term reproductive endocrine bioassay using steroid hormone and vitellogenin end points in the estuarine mummichog (Fundulus heteroclitus).

We have developed a short-term gonadal recrudescence test with the estuarine mummichog (Fundulus heteroclitus) and determined endocrine end points sensitive to a strong estrogen agonist (ethynylestradiol; EE2) and an antiestrogen (ZM 189,154; ZM) at concentrations of 0 to 1,000 ng/L in three separate experiments. A protocol was developed to ensure a year-round supply of recrudescing fish. A protocol for determining steroid production (testosterone and 11-ketotestosterone [11-KT] in incubated testes tissue and testosterone and 17-estradiol [E2] in incubated prematurational follicles) was optimized. Recrudescing fish (males, gonadosomatic index = 2%; females = 10%) were exposed to graded doses of EE2 or ZM for 7 to 15 d using a static daily-renewal protocol. At high EE2 (>250 ng/L), the effect on males was depression of androgen steroidogenesis and plasma steroid levels. In females, high EE2 depressed gonadal production and circulating E2 levels; however, EE2 concentrations <100 ng/L caused increased gonadal production and plasma E2. Low ZM (<100 ng/L) had little effect on male and female fish, while higher concentrations (>250 ng/L) increased E2 and 11-KT production while decreasing plasma 11-KT and E2 (1,000 ng/L only). Male and female plasma vitellogenin responded in a concentration-dependent fashion to EE2 with no effect by ZM. The low observable effect concentrations for the endocrine parameters were 1 ng/L for EE2 and 250 ng/L for ZM. The bioassay and results encompassing the environmentally relevant exposure range (1-100 ng/L) will be useful for assessing effects of endocrine-active contaminants in estuarine environments.