California Sea Grant College Program

A large body of work has established a link between endocrine disrupting compounds (EDCs) and physiological abnormalities in fishes. EDCs, which include pesticides such as pyrethroids, can mimic, synergize or antagonize the effects of endogenous hormones. Both theory and empirical data confirm that EDCs can also cause fish population decline. However, to date few studies have attempted to link realistic environmental EDC mixtures with responses at multiple tiers of the biological hierarchy, including population level impacts. Additionally, although EDCs currently areknown to impact a wide array of fishes, most studies continue to use a few standardlaboratory denizens. A need exists for an estuarine model fish, particularly consideringthat estuaries are utilized by many fish species for part of their lives and are subject to many EDC inputs. Silversides (Menidia spp.) are well appointed for this role.Furthermore, the San Francisco Bay (SFB) estuary, home to introduced silversides,represents an ecosystem in need of a surrogate to evaluate EDC impacts. As such, an assessment of SFB’s Suisun Marsh, an area with documented pyrethroid presence and EDC inputs, using silversides was undertaken. The first objective was to establish Menidia species as an EDC bioindicator. The second objective was to measure environmental impacts at multiple biological scales and use correlations between scales to discern potential mechanisms of disruption. The third objective was to develop and utilize techniques in the laboratory to further understanding of EDC environmental impacts. Clear links were observed between the biological scales examined for signs of endocrine disruption in Menidia at two sites within Suisun Marsh of the SFB estuary, which included alterations in sex ratio, gonadal morphology and expression of estrogen responsive genes. Additionally, my findings suggest that the pyrethroids bifenthrin and permethrin are contributing to the incidence of endocrine disruption in SFB fishes. Finally, I developed a whole body homogenate ELISA that allows the detection of Menidia choriogenin, an estrogen responsive protein, in these small fish from which plasma cannot be obtained. Ultimately this work establishes Menidia spp. as a sensitive EDC bioindicator and expands the universe of responses that may be evaluated in both the field and the lab.