Genetic Basis for Thermal Tolerance in Two Different Strains of Rainbow Trout (Oncorhynchus mykiss): Case Western and Kamloops

This thesis examines the thermal tolerance based on how expression of Heat Shock Protein (HSP) 70 and HSP90 differ between two different strains of rainbow trout (Oncorhynchus mykiss), the Case Western strain and the Kamloops strain, and determines if cortisol levels affect HSP expression in red blood cells. The Case Western strain is considered the only warm water trout, only recently was any aspect of its thermal tolerance quantified. Porto (2012) determined critical thermal maxima (CTM) for the Case Western strain and found it to be about 0.15 °C higher than the Kamloops strain. This thesis is comprised of three chapters: (1) an introduction and literature review on the biological history of these two strains of rainbow trout, on studies related to HSPs expression as indicators of thermal tolerance, and studies on the relation between cortisol expression and HSPs expression; (2) an experimental study investigating the differences between HSP70 and HSP90 between the two strains, before and after a heat stress test and between individuals of different sizes; (3) an experimental study investigating the relation between the heat stress protein expression and cortisol levels pre- and post-stress. The results on the HSP70 and HSP90 relative expressions confirm that Case Western strain has higher thermal tolerance, highlighting the importance of this strain as a candidate to be cultured in aquaculture facilities as an answer to possible impacts of future climate changes. Earlier studies suggested HSP expression varied with age in rainbow trout, but failed to consider strain-specific differences. Our results show that age-specific HSPs expression is not species-specific in rainbow trout as it differs by strain. The results show that the plasma cortisol levels before and after thermal stress do not differ among strains, and that the physiological response to heat stress is species-specific. The variable that has the largest influence on the variance expressed among groups came from the HSP90 gene. We found the stressed Kamloops was the most diverse group, with less thermal tolerance, influenced mostly by the weight of the HSP90 on the total variance