Degree Name

Master of Science (MS)

Semester of Degree Completion


Thesis Director

Anabela Maia


Fish natural habitats are increasingly contaminated with various estrogenic compounds, including 17β estradiol (E2). This compound causes adverse effects on the reproductive system of male fish; however, the effects of E2 on other aspects of fish metabolism, morphology and histopathological changes in internal organs are not well known. The objective of this study is to evaluate the effects of E2 exposure on the basal and stressed metabolic rate, morphological changes in body shapes, and histological changes in the liver tissues of sunfish species. Fish were held individually in ten gallon tanks under two treatments of 40 and 80 ng/L and one control treatment (no E2). The duration of E2 exposure was 21 days, with E2 being replenished every week based on its half-life. Basal and maximum aerobic scopes were measured using closed respirometry and a chase protocol at the beginning and at the end of the experiment. Lateral pictures of the fish were also taken at these two time points. My working hypotheses are that (1) fish subjected to E2 exposure would experience stress and thus increased oxygen consumption, (2) male dimorphic characters would become less noticeable in exposed fish, and (3) there would be alterations in the structure of liver hepatocytes after E2 exposure. I found that the basal metabolic rate decreased after 21 days in the control group but not in the estradiol exposed groups. In terms of morphological changes, I observed reduction in operculum size and decrease in head size in exposed individuals but not in the control. Some morphological changes in male-related characters in sunfish which eroded male dimorphic characters were caused by E2 exposure. Preliminary histological examination of liver tissues showed that there was a disintegration of hepatocytes in the E2-exposed liver tissues. My research highlights negative effects of estradiol that are more widespread than simple gonadal alterations which warrant close monitoring of estradiol contamination in the natural water system.