Date of Award

8-2017

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Heather Hamlin

Second Committee Member

Ian Bricknell

Third Committee Member

Mary Tyler

Additional Committee Members

Adria Elskus

David Berlinsky

Abstract

Embryo mortality of Atlantic salmon, Salmo salar Linnaeus 1758, has been increasing for more than a decade in the State of Maine, a leading producer of this species in the United States. Increasing embryo mortality not only creates a financial bottleneck for farms but also prevents the sale of surplus eggs as an additional source of revenue. Blood and egg samples were collected at three Maine Atlantic salmon farms from female broodstock at the time of spawning over a 2-year period. Correlative factors for reduced embryo survival were investigated by measuring egg and maternal plasma concentrations of 17-estradiol (E2), 11-ketotestosterone (11-KT), testosterone and calcium, as well as maternal hepatic ethoxyresorufin-O-deethylase (EROD) activity and standard length. Significant positive correlations were found between maternal plasma concentrations of E2 and 11-KT and embryo survival. Interestingly, there was no correlation with egg concentrations of sex steroids and embryo survival, suggesting that embryo mortality does not likely rest with the maternal deposition of sex steroids into the egg, but with another hormone regulated process related to egg assembly, ovulation, or post-ovulatory ageing. iv E2 and 11-KT in the plasma, ovarian fluid (OF) and eggs of female broodstock Atlantic salmon were measured to determine possible sources of sex steroids to the eggs. There was a positive correlation between OF hormone concentration and egg hormone concentration but no correlation between maternal plasma hormone concentration and egg hormone concentration, suggesting OF plays an important role in oocytes at the time of spawning. Although the correlations in this study help us to understand the reproductive biology of the Atlantic salmon, this information applies only to the time of spawning. Therefore, annual hormone profiles of the northern strain of Atlantic salmon were created by plotting monthly average hormone concentrations of plasma E2 and 11-KT in female broodstock Atlantic salmon over the course of a year to better understand the reproductive biology of this commercially important species.

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