2006. Differences in Ichthyophonus prevalence and infection severity between upper Yukon River and Tanana River chinook salmon, Oncorhynchus tshawytscha (Walbaum), stocks

• Main Authors: R Kocan, P Hershberger
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Alaska; Canada; chinook salmon; Ichthyo- phonus; Tanana River; Yukon River; Yukon; Yukon river
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.585.4411; http://rapidsresearch.com/Kocan_Hershberger_Yukon-Tanana_ICH.pdf

Two genetically distinct populations of chinook salmon, Oncorhynchus tshawytscha (Walbaum), were simultaneously sampled at the confluence of the Yukon and Tanana rivers in 2003. Upper Yukon-Canadian fish had significantly higher infection prevalence as well as more severe infections (higher parasite density in heart tissue) than the lower Yukon-Tanana River fish. Both populations had migrated the same distance from the mouth of the Yukon River at the time of sampling but had sig-nificantly different distances remaining to swim before reaching their respective spawning grounds. Multiple working hypotheses are proposed to explain the differences between the two stocks: (1) the two genetically distinct populations have dif-ferent inherent resistance to infection, (2) genetic-ally influenced differences in feeding behaviour resulted in temporal and/or spatial differences in exposure, (3) physiological differences resulting from different degrees of sexual maturity influenced the course of disease, and (4) the most severely infected Tanana River fish either died en route or fatigued and were unable to complete their migra-tion to the Tanana River, thus leaving a population of apparently healthier fish.