Fish reproduction: An ecologically relevant indicator of endocrine disruption

Endocrine-disrupting compounds have the potential to alter hormone pathways that regulate reproductive processes. With the exception of endocrine effects leading to reproductive impairment and population declines ill a few wildlife species (e.g., Great Lake [USA] bald eagles, Lake Apopka [Florida, USA] American alligators), the ecological implications of exposure to endocrine disrupting compounds has not been adequately investigated. For example, male fish exposed to estrogenic compounds show induced production of vitellogenin, an egg yolk precursor, but the biological significance of elevated vitellogenin levels is speculative. The development of techniques to predict and more accurately assess the ecological relevance of exposure to endocrine-disrupting compounds is needed. In this review, we focus on fish reproduction as an ecologically relevant indicator of endocrine disruption, specifically estrogenic activity. The following will provide a brief review of gonochoristic reproductive and endocrine physiology, as well as outline some of the commonly used techniques to screen for estrogenic activity in fish. Last, a proposed model reproductive assay using Japanese medaka (Oryzias latipes) is presented.