Juvenile chinook salmon (Oncorhynchus tshawytscha) were experimentally infected with Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease (BKD), to investigate the effects of BKD on three aspects of juvenile salmonid performance: (1) predator avoidance ability; (2) smoltification; and (3) physiological responses to stress. For these experiments, fish with different Rs-infection profiles (created by using an immersion challenge method) were sampled to assess physiological change and subjected to various performance tests during disease progression. When equal numbers of Rs-challenged and unchallenged fish were subjected to predation by northern pikeminnow (Ptychocheilus oregonensis) or smallmouth bass (Micropterus dolomieui), Rs-challenged fish were eaten in significantly greater numbers than controls by nearly two to one. A progressively worsening infection with Rs did not alter the normal changes in gill ATPase and condition factor associated with smoltification in juvenile chinook salmon. A dramatic proliferation of BKD was associated with maximal responses of indicators of smoltification, suggesting that the process of smoltification itself can trigger outbreaks of disease. When Rs-infected fish were subjected to three 60-s bouts of severe handling that were separated by 48-72 h, this experience did not lead to higher infection levels or increased mortality when compared to diseased fish that did not receive the stressors. Furthermore, the kinetics of plasma cortisol, glucose, and lactate over 24-h following each stressor were similar between fish with moderate to high BKD and those that had low or no detectable infection. Fish with moderate to high Rs infections had higher titers of cortisol and lactate prior to each application of the stressor and were also unable to consistently elicit a significant hyperglycemia in response to the stressors when compared to fish with low infection levels. During all experiments, fish consistently developed decreased hematocrits and blood glucose levels and increased levels of cortisol and lactate as the disease worsened, indicating that BKD is stressful, particularly during the later stages. Collectively, these results illustrate the impact of BKD on juvenile salmonids and have also ascribed some ecological significance to this disease beyond that of direct pathogen-related mortality. / Graduation date: 1999

Genetic differences between early and late forms of Alaskan chinook salmon (Oncorhynchus tshawytscha) were identified using two genetic approaches: mitochondrial DNA (mtDNA) analysis and protein electrophoresis. The study populations consisted of early- and late-run chinook salmon in each of the Kenai and Kasilof rivers in Alaska, and a single population from the Minam River, Oregon, that provided a relative scale for the differences among the Alaskan populations. Two segments of mtDNA were amplified separately using the polymerase chain reaction (PCR) and then digested with 14 to 16 restriction enzymes. Results showed that the two early runs were genetically similar to each other but different from either of the late runs. The late runs were different from each other based on the frequency of the common haplotypes. The Minam River stock shared two haplotypes with the Alaskan stocks and displayed one unique haplotype. The frequency difference in the shared haplotypes together with the presence of a unique haplotype allowed us to separate the Oregon population from those in Alaska. In the protein analysis, each of the five populations was examined at 30 allozyme loci to determine variation within and between the runs. Based on 14 polymorphic loci, Minam River chinook salmon were genetically distinct from the Alaskan populations. Within the Alaskan populations, the two early runs were most similar to each other but different from the two late runs; the two late runs were also genetically most similar to each other. Based on all loci, protein electrophoresis proved to be a useful technique to separate stocks of chinook salmon. On a locus by locus basis, however, mtDNA was more powerful. Both mtDNA and allozyme analysis suggest that chinook salmon may segregate into genetically different early and late forms within a drainage. / Graduation date: 1995

Three experiments were designed to determine if and how steelhead trout, Oncorhynchus mykiss, may affect chinook salmon, O. tshawytscha, when they are confined together as in a raceway or on a barge. We observed groups of chinook and steelhead together and groups of only chinook in a behavioral experiment to determine if steelhead are aggressive and if their presence changed the behavior of chinook. Two physiological experiments were completed to determine if the loading of steelhead on top of chinook and if the introduction of odor from rainbow trout (steelhead not available) caused a change in plasma cortisol levels in chinook. It was found that chinook showed characteristics of a schooling species, while steelhead exhibited territory holding characteristics. Behavioral changes in chinook were observed when steelhead were present. Chinook grouped with steelhead reduced their movements, darted less, were attacked up to 16 times more often, and were found less frequently in the shade than groups of only chinook. Steelhead were found to establish territories and defend them with chases, charges, and nips. In attempts to establish territories and defend them, steelhead attacked chinook as often as they attacked other steelhead even though chinook showed little aggression toward steelhead. In a physiological experiment, chinook experienced the loading of salmonids into their tank. Chinook had higher levels of plasma cortisol at 2 and 32 hours after the loading of steelhead than chinook that were loaded with chinook or controls (no loading). A second physiological experiment with odor showed that chinook that received rainbow odor and those that received chinook odor had similar levels of plasma cortisol. Cortisol levels (two hours after the odor was introduced) were higher in chinook receiving either of the scented waters than in those that did not receive any odor. In conclusion, all three experiments indicated that the presence of juvenile steelhead trout affect juvenile chinook salmon behavior and physiology. / Graduation date: 1998