Effects of endocrine -disrupting chemicals on fish reproduction and reproductive indicators

The central hypothesis tested in this dissertation is that endocrine-disrupting chemicals (EDCs) found in the aquatic environment disrupt reproductive processes in fish. To gain a broad perspective of existing evidence, a review of the current literature was conducted. From this literature review, the lack of a dependable method or indicator to assess reproductive fitness of fish in situ was identified as an outstanding need. In laboratory experiments, reproductive endpoints (egg production, fertility and viablity) were measured in the marine fish Tautogolabrus adspersus , or cunner, implanted with estrogens. Estrone and ethynylestradiol significantly reduced egg production in treated cunner at the highest implanted concentration. Estradiol had no significant effects on any reproductive parameter when compared to controls. The applicability of male plasma vitellogenin as an indicator of reproductive dysfunction in estrogen-treated cunner was investigated. Results suggest that male plasma vitellogenin is not a reliable indicator of reproductive impairment. Because steroidogenesis is critical to normal reproductive processes, changes in the activity of steroidogenic enzymes might serve as a discerning indicator of reproductive dysfunction. As a preliminary test of this hypothesis, changes in the activity of aromatase were measured in the brains and gonads of cunner exposed to atrazine, an EDC that does not bind with the estrogen receptor but appears to interfere with normal steroidogenesis. Aromatase catalyzes the conversion of androgens to estrogens. In atrazine-treated cunner, reproduction (egg production, fertility and viability) was significantly decreased and brain aromatase activity significantly increased in one atrazine treatment. To further explore the hypothesis that aromatase activity could be used as an indicator of reproductive dysfunction in fish, cunner were exposed to a variety of EDCs, including estradiol, ethynylestradiol, octylphenol and androstatrienedione (an aromatase inhibitor). Reproductive endpoints were compared to brain and gonad aromatase activity in exposed fish. Results indicate that changes in male brain aromatase activity is a reliable indicator of exposure to all of these EDCs. Modulation of aromatase activity in the brains of spawning male cunner exposed to these EDCs was also consistently linked with reproductive impairment in these fish