| Summary: | Male hornyhead turbot (Pleuronichthys verticalis ) living in Santa Monica Bay exhibit extraordinary plasma concentrations of the active estrogen, 17β-estradiol (E2), comparable to concentrations typically measured in reproductively active female fish. In contrast, when turbot males are collected from an environment 25 km south, in Orange County, their plasma E2 concentrations are substantially reduced. Furthermore, when they are transferred from the bay and placed into aquaria containing clean seawater, the high-E2 phenotype subsides. At 4 and 8 weeks after transfer, the fish show decreased testicular mRNA expression of steroidogenic enzymes involved in E2 production, along with decreased plasma E2 concentrations. The findings suggest that environmentally-induced alterations in testicular steroidogenesis may underlie endogenous E2 production in the males, leading to elevated E2 levels. Data also implicated the steroidogenic enzyme 17β-HSD-1 as a possible target of the environmental effect, since its increased expression can result in enhanced E2 production.
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