Otolith Tools in the Ecotoxicology Toolbox: Unraveling Sources and Pathways of Se Exposure in Wild Sacramento Splittail with Spinal Deformities

Selenium (Se) is an essential nutrient required for oxidative and enzymatic processes, but at elevated levels it can disrupt protein synthesis resulting in deformities in developing offspring of fish and birds. Incidences of individuals with deformities consistent with Se toxicity (e.g., S-shaped spines) have been observed in Sacramento splittail (splittail) Pogonichthys macrolepidotus, a cyprinid endemic to the San Francisco Estuary and its watershed.  Juvenile splittail can be exposed to elevated Se through direct ingestion of prey or through maternally-derived yolk.  Here, we use scanning X-ray fluorescence microscopy (SXFM) at Cornell’s High Energy Synchrotron Source to detect Se and quantify the chronology of Se in otoliths of wild-caught juvenile splittail that display spinal deformities.  We evaluate the spatio-temporal distribution of Se in the otoliths and compare the core (maternal) and edge (environmental) to test the pathway of Se exposure.  Results of this study demonstrate the utility of otolith tools in ecotoxicology to differentiate among multiple human-mediated sources of elevated Se in the ecosystem that can influence native fishes.