Development of an in vivo screening assay for estrogenic chemicals using juvenile rainbow trout (Oncorhynchus mykiss)

In this study, the Organisation for Economic Cooperation and Development (O ECD) Test Guideline 204 was adapted for the development of an in vivo scree n for detecting estrogenic activity using juvenile rainbow trout (Oncorhync hus mykiss). The influence of feeding ration and the effect of reference es trogenic chemicals on somatic growth, gonadosomatic index, hepatosomatic in dex, and plasma vitellogenin concentrations were evaluated over 21 d. A fee ding ration of 4% body weight per day resulted in temporal increases in bod y weight, hepatosomatic index, and plasma vitellogenin concentration in bot h males and females. A feeding ration of 1% did not induce any changes in t he measured endpoints and was adopted for the subsequent estrogen exposures . Exposure of juvenile female fish to 17 beta -estradiol and 4-tert-nonylph enol produced concentration-dependent inductions of plasma vitellogenin tha t were optimal after 14 d, with lowest observed effect concentrations of 8. 9 ng/L and 16 mug/L, respectively. Methoxychlor also induced synthesis of p lasma vitellogenin with a 14-d lowest observed effect concentration of 9.8 mug/L. Higher concentrations of methoxychlor were toxic to fish. Increases in the hepatosomatic index occurred on day 14 in fish exposed to 244 ng/L 1 7 beta -estradiol and 53 mug/L 4-tert-nonylphenol. None of the compounds te sted caused detectable changes in the gonadosomatic index. Vitellogenin ind uction in juvenile trout was sensitive to estrogenic chemicals, occurred ra pidly, and the response was highly consistent between experiments (coeffici ent of variation = 4.5% for the 17 beta -estradiol positive control). The 1 4-d juvenile fish assay offers a sensitive and robust in vivo screening met hod for estrogen-active substances.