College of Science and Health Theses and Dissertations

Date of Award

Fall 11-24-2020

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Science

First Advisor

Jason Bystriansky, PhD

Second Advisor

John Dean, PhD

Third Advisor

Windsor Aguirre, PhD

Abstract

Juvenile chinook salmon (Oncorhynchus tshawytscha) encounter a variety of environmental conditions on their migration from freshwater to the ocean. These migrations are physiologically demanding, requiring salmon to reverse their osmoregulatory strategies to successfully acclimate to changing salinity. This reversal occurs primarily at the gills (main osmoregulatory organ) where respiratory and osmoregulatory functions are occurring simultaneously. When subjected to a physiological stressor, the gills will compromise in design to alleviate the most limited function. This tradeoff is known as the ‘osmorespiratory compromise’. This thesis examined whether an osmorespiratory compromise in chinook salmon induced by sustained exercise (a gas exchange stressor) would lead to secondary changes in gill function that would enhance the fish’s ability to acclimate from freshwater to saltwater (an osmoregulatory stressor). In this thesis, plasma total osmolality and ion concentrations, white muscle water content, gill Na+/K+-ATPase (NKA) and gill NKA α-subunit isoform mRNA expression were measured on exercised and non-exercised fish in freshwater, as well as exercised and non-exercised fish exposed to a 7-day salinity challenge. Exercise did not induce any notable impairment to ion balance or gill NKA activity after 20 days of being swum at ~1 body length/second (BL/s) in fish that remained in freshwater, but exercised fish did have a significantly higher white muscle water content than non-exercised fish. Both exercised and non-exercised fish exposed to saltwater experienced a characteristic rise in total plasma osmolality and ion concentrations, followed by a recovery to freshwater levels, with exercised fish demonstrating a clear trend of lessened osmoregulatory disturbances compared to non-exercised fish. Interestingly, exercised fish were able to significantly upregulate gill NKA activity and the proposed saltwater α-subunit isoform (α1b) mRNA levels quicker than non-exercised fish, which may explain why exercised fish ix experienced less disturbance to osmoregulatory status. These results imply that a sustained exercise training period prior to saltwater exposure improves saltwater acclimation in chinook salmon.

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