Date of Award

2005

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Zoology

Advisor

Terry Haines

Second Committee Member

Rebecca Holberton

Third Committee Member

Rebecca Van Beneden

Abstract

Since the early 19801s, the numbers of adult Atlantic salmon (Salmo salar) returning to Maine's rivers have been in a general decline. In addition, estimates of parr, freshwater smolt and emigrating smolt populations indicate low overwinter survival rates. Overall, these low numbers, along with several other factors, resulted in the Atlantic salmon in eight rivers in Maine being classified as a distinct population segment under the Endangered Species Act. Because many of the listed rivers are found near lowbush blueberry barrens, I investigated the endocrine disrupting potential and effects of selected blueberry pesticides on Atlantic salmon. An E-SCREEN assay was conducted to determine the relative estrogen mimicking properties, measured by a relative proliferative effect, of the most commonly used pesticides registered for use on lowbush blueberry. Atlantic salmon (Salmon salai) pre-smolts of hatchery origin were subjected to pulsed exposures of a mixture of pesticides at environmentally realistic concentrations. For each of the two years of this study, pre-smolts were subjected to a total of five weekly, 24 h pesticide exposures. In Year One, Velpar (hexazinone), Orbit (propiconazole), and Super BK (2,4 Dichlorophenoxy acetic acid) were tested. In Year Two, Orbit, Sinbar (terbacil), and lmidan (phosmet) were tested. To evaluate the effects of the pesticides on smoltification, the fish were periodically exposed to 24 h saltwater challenge tests (SWCT) to examine the osmoreg~~latoaryb ility of the pre-smolts. Gill Na'/K"-ATPase activity, plasma chloride concentration, hematocrit, vitellogenin presence, and plasma steroid concentrations (estrogenlandrogen) of randomly selected smolts were measured after the pesticide exposures and saltwater challenges. Control group Atlantic salmon pre-smolts did undergo smoltification as indicated by increased gill Na'/K'-ATPase activity and low mortality rates in SWCT. Body length and weight of smolts was not affected by pesticide exposure in either year. Significantly lower gill Na'/K+-ATPase activity was detected in smolts during Year Two only after the second SWCT. Plasma chloride levels were significantly different between control and exposed groups for both years, but overall values in each treatment remained in expected ranges for freshwater and saltwater portions of the study. Hematocrit values were within the normal range in Year One, but in Year Two exposed fish had significantly higher values than control fish after each pesticide exposure. Plasma steroid concentrations did not significantly differ between groups for either year. Therefore, in spite of multiple pulsed exposures to mixtures of blueberry pesticides calculated to be above expected concentrations found in the environment, the results do not support the hypothesis that the observed overwinter mortality of smolts and reduced adult returns of Atlantic salmon are due to endocrine disruption by the pesticides utilized in this study.

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