Journal of Aquatic Animal Health 16:58–72, 2004 Copyright by the American Fisheries Society 2004 Ichthyophoniasis: An Emerging Disease of Chinook Salmon in the Yukon River

• Main Authors: Richard Kocan, Paul Hershberger, James Winton
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Canada; Pacific; Yukon; Yukon river; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.539.5215; http://rapidsresearch.com/YukonIchKocan.pdf

Abstract.—Before 1985, Ichthyophonus was unreported among Pacific salmon Oncorhynchus spp. from the Yukon River; now it infects more than 40 % of returning adult Chinook salmon O. tshawytscha. Overall infection prevalence reached about 45 % in the Yukon River and about 30% in the Tanana River between 1999 and 2003. Mean infection prevalence was greater in females than males in the main-stem Yukon River during each of the 5 years of the study, but the infection prevalence in males increased each year until the difference was no longer significant. Clinical signs of ichthyophoniasis (presence of visible punctate white lesions in internal organs) were least at the mouth of the Yukon River (;10%) but increased to 29 % when fish reached the middle Yukon River and was 22 % at the upper Tanana River. However, clinical signs increased each year from 7 % in 1999 to 27 % in 2003 at the mouth of the river. As fish approached the upper reaches of the Yukon River (Canada) and the spawning areas of the Chena and Salcha rivers (Alaska), infection prevalence dropped significantly to less than 15 % in females on the Yukon River and less than 10 % for both sexes in the Chena and Salcha rivers, presumably because of mortality among infected prespawn fish. Age was not a factor in infection prevalence, nor was the position of fish within the run. The source of infection was not determined, but Ichthyophonus was not