Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)




Patty Zwollo

Committee Member

Diane Shakes

Committee Member

Drew M. LaMar


Pacific salmon migrate long distances to spawn as part of their life cycle. During this journey from sea to their natal stream, they undergo major endocrine, physiological and immune changes. Cortisol, the primary stress hormone, gradually increases during the journey. Persistent high cortisol levels have deleterious health effects, including suppression of the antibody response. However, pathogens encountered during their journey may stimulate antibody responses to overcome the infection. My main research question focuses on how salmonids balance the immunosuppressive effects of high cortisol levels with activation of the antibody response. A recent field study from our lab showed a transient increase in abundance of B cells during the spawning run which is suggestive of activation of the immune system during this journey. However, our field study had too many confounding variables. In this study, we investigated the activation of the antibody response under conditions of elevated levels of cortisol in rainbow trout under laboratory-controlled conditions. We looked at the effects of a) cortisol alone, b) fish pathogen Flavobacterium psycrophilum (Fp) alone and c) combined cortisol and Fp challenge on the gene expression of immunoglobulins IgM and IgT using qPCR. We have found that cortisol suppresses the IgM response in the spleens of Fp-susceptible line but not in Fp-resistant line of Rainbow trout. No significant effects on B cell development where observed in the anterior kidney. Taken together, our data suggest that the antibody response in Fp-resistant rainbow trout is less sensitive to increased cortisol levels compared to Fp-susceptible fish, confirming our hypothesis that Fp-resistant fish have in some way evolved to manage stress more successfully.




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