Headquarters, Seattle Laboratory
Research on impact of Ichthyophonus
Research on the impact of Ichthyophonus that is affecting subsistence fisheries for Chinook salmon by Alaskan natives. Reports from subsistence fishermen and tribal elders indicate the emergence of Ichthyophonus infections in adult Chinook salmon returning to the Yukon River in Alaska are associated with adverse flesh quality and possible pre-spawning losses. Researchers from the Western Fisheries Research Center examined Chinook at multiple sites within the Yukon system and found clinical signs of disease were minimal when fish entered the river, but increased significantly when fish reached the middle river. Among fish from the end of the run, the parasite was disseminated and clinical disease was apparent in multiple organs, especially the heart; however, female spawn-outs had lower levels of Ichthyophonus suggesting the most severely diseased fish had died before spawning. Elevated river temperatures in recent decades were postulated to be an important cause of the emergence and increased severity of the disease.
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