The effects of strain and ploidy on the physiological responses of rainbow trout (Oncorhynchus mykiss) to pH 9.5 exposure

British Columba (BC) has a well-established lake-stocking program that relies on hatchery-reared rainbow trout (Oncorhynchus mykiss) from multiple wild and domesticated strains. These strains are stocked into BC lakes as diploids and triploids and, in general, high mortality rates are common after lake stocking due to environmental conditions. Of particular concern is that some lakes in BC are approaching a pH of 9.5, and it is not known if strain and ploidy affects the physiological responses of trout to high pH exposure. The goal of this thesis is to understand the effects of pH exposure, in both soft and hard water, on wild and domestic strains of trout as diploids and triploids. In soft water, high pH exposure resulted in more than 40% loss of equilibrium in the wild strains of trout while the Fraser Valley domesticated strain had fewer than 10% of individuals lose equilibrium overall. There were no clear differences between ploidies in loss of equilibrium. High pH exposure caused significant increases in plasma and tissue ammonia, with no differences between strains or ploidies in ammonia accumulation. In the brain, glutamine increased in response to high pH exposure and glutamate decreased suggesting a protective mechanism of glutamine production in high pH. Plasma lactate accumulated in all groups, suggesting an increase in anaerobic metabolism as a result of high pH exposure. There were no physiological differences between high pH exposure in hard and soft water among the strains tested. However, triploid rainbow trout suffered a greater loss of equilibrium than diploid trout, occurring in conjunction with a significant elevation of brain ammonia in triploid rainbow trout when compared to diploid trout in high pH water. Overall, the results of this thesis demonstrate an effect of strain on high pH tolerance in trout, but the differences in tolerance appear to not be explained by differences in ion regulation and ammonia balance.Science, Faculty ofZoology, Department ofGraduat