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Abstract
Reports of intersex fish (males with oocytes in their testicular tissue) in water bodies around the world have stimulated widespread concern about the effects that chemicals are having in the environment. Estrogens and estrogen-like chemicals in the environment are known to induce intersex and other forms of endocrine disruption in fish. Intersex fish can have decreased sperm production, decreased sperm motility and decreased fertilization success compared to histologically normal male fish. The aquatic environment may contain a host of endocrine disrupting chemicals. Complex chemical mixtures associated with wastewater effluent, agricultural and industrial run-off all pose a threat to fish from egg fertilization to spawning. Endocrine disruptors can mimic sex hormones in humans, terrestrial wildlife and aquatic organisms and endocrine disruptors of particular concern are the natural and synthetic estrogens, and estrogenic compounds. My experiments address hypotheses regarding the distribution and incidence of intersex largemouth bass in Georgia and possible factors contributing to this condition. Both lab and field based projects were performed to explore relationships among possible environmental influences, background rates of intersex and endocrine disruption in fish. A survey of intersex largemouth bass, waterborne estrogens and estrogenic potency in impoundments across Georgia provided valuable information about the spatial distribution of the condition, the potential background rate of intersex in basses, and characteristics of waters associated with high rates of intersex. Laboratory-based experiments explored possible contributing factors to endocrine disruption in fish including sediment lifecycle exposures with sediment collected from high intersex impoundments. Hierarchical modeling with AICc for model selection was used for predicting the probability of an intersex fish present in a water body. Without conclusive evidence that estrogens or sediment-bound estrogens were playing a substantive role in endocrine disruptions, the ubiquitous pollutant nitrate was investigated as a potential causative factor as many of the smaller impoundments were highly eutrophic. Results from this project describe the distribution of intersex largemouth in Georgia impoundments. Intersex fish are most likely found in small, shallow impoundments where estrogenic exposure and other endocrine disrupting chemicals may or may not be heavily involved.