In the lower Yukon this disease usually is found in the beginning stages. Fishers often never see the effects and biologists are often unable to accurately detect the infection prevalence. In the middle Yukon the disease starts to become visible in the heart and flesh of those infected, and infection and disease prevalence can now be accurately looked at. Prevalence has been as high as 45% in females some of the monitored years but some of the worse years were prior to any monitoring in the early and mid 1990’s. In the upper Yukon around the confluence of the Tanana River and above each year, it’s severity is often the reason the Chinook subsistence fishery ends before the Chinook stop running. In the headwaters and spawning grounds exists the political/biological question of whether all those diseased fish made it or not, and the effects on present day runs. Ichthyophonus today is one of the most divisive issues in the drainage. Marketing, management, subsistence interests, and even “scientific” research all seem to get caught in it grips. Below are some of the media stories that have come out about ICH.
Link to Los Angeles Times National News Story and Video (June 15, 2008):
Alaska Salmon may bear scars of global warming
Los Angeles Times reporter Ken Weiss talks with Bruce Gellerman
about Ichthyophonus - (June 20 2008)
Click for Living on Earth - NPR Interview
Link to Alaska Public Radio Interview (February 29, 2008):
Salmon Parasite may be on the rise in Yukon River
Sometimes it takes good eyes to see the smaller Ichthyophonus “spores” in hearts. Click on left picture to view enlarged picture and see ICH. Right picture is a diseased liver with large “spores” (both Chinook)
With the disease’s tendency to advance much faster in the larger salmon one can wonder (along with other possible factors) how much it is linked to the decline and present day lack of the older Chinook age classes (see graph below). While the problem of Chinook size decline started around the time Ichthyophonus disease in the Yukon became pronounced, present studies, data collection and monitoring are not consistent or focused enough to speak to that issue
Above graph shows linear increase in clinical ichthyophoniasis with increasing fish size over
a 7-year period.
One of the latest findings was published in a recent article in the Transactions of the American Fisheries Society (Zuray et al. 2012) and described a multi-year epidemiologic study of ichthyophoniasis in Yukon River Chinook salmon from 1999 to 2010 that revealed a strong correlation between changes in disease prevalence and population abundance. Both run size and ichthyophoniasis increased and decreased simultaneously (i.e. were concordant); the greatest concordance occurring among females, where the two values rose and fell synchronously for 10 of 11 years (91%) (X2 = 0.003). Although there was no cause-and-effect relationship, the strong correlation between the two values made it a good model for predicting changes in run size based on increases or decreases in ichthyophoniasis (and visa versa). Since 2010 two additional years of data were added to the model, and as predicted, when ichthyophoniasis increased, so did run size, and when it fell, run size declined. The graph below compares data on increases/decreases in disease and run size from 2004 through 2012 showing the continuing correlation between ichthyophoniasis and run size.
It is generally thought that water temperature in the Yukon River during the migration
period has a direct bearing on the severity an Ichthyophonus infected fish will become diseased. Below is a severe disease condition in a Chinook filet.
Disease Rates over the years
Below graph is a 12-year summary of clinical ichthyophoniasis in Yukon River Chinook salmon collected during two consecutive studies. Infection prevalence peaked in 1999, 2003 and 2006, followed by a steady decrease through 2010. While no data exists for years prior to 1999 most fishermen remember the mid 90’s as being the worse with large amounts of diseased king being discarded and prevalence in females well beyond 50%.
The disease will continue running it’s course each year. Hopefully after numbers of fish generations the Chinook will build a resistance to it. Because of variables of water temperature and what part of the run the fish migrates upriver in (see graph below) is very important to do consistent, yearly, full season disease monitoring, and disease prevalence testing upriver of the mouth. Without these basics we’ll have no more of an educated idea of it’s effects in the future than we do of it’s past and present.
Above graph shows change in clinical Ichthyophoniasis (%) in Yukon River Chinook salmon during their upriver spawning migration. The increase in disease prevalence corresponds with the observations of local fishers who annually report higher numbers of diseased fish near the end of the run.
Open a report below for viewing by left click on report or download a copy by right click and then select save target as)
Yukon River Chinook Ichthyophonus Reports
Note: Some of the below reports are published peer reviewed papers, others are simply project reports or critical reviews of those reports. In order to better understand this divisive issue an effort will be made to list a variety of differing opinions. Please contact for inclusion of any you think valuable.
” Just Out” Ichthyophonus-infected walleye pollock Theragrachalcogramma (Pallas) in the eastern Bering Sea: a potential reservoir of infections in the North Pacific
V C White1, J F Morado1 and C S Friedman2
PCR is Still Inappropriate as a field Diagnostic Tool, 2013,
Richard M. Kocan, Ph.D., Professor Emeritus, School of Aquatic & Fishery Science
University of Washington
PCR testing can be as accurate as culture for diagnosis of Ichthyophonus hoferi in Yukon River Chinook salmon, Hamazaki, Kahler, Borba, Burton,
Diseases of Aquatic Organisms, 2013
Proposed Changes to the Nomenclature of Ichthyophonus sp. Life Stages and Structures, R. M. Kocan, School of Aquatic and Fishery Sciences, Univ. of Wash., Seattle, Washington, American Society of Parasitologists 2013
Evidence for an Amoeba-Like Infectious Stage of Ichthyophonus sp. and
Description of a Circulating Blood Stage: A Probable Mechanism for Dispersal
Within the Fish Host, Kocan, LaPatra, and Hershberger
Journal of Parasitology, 2013.
Synchronous Cycling of Ichthyophoniasis with Chinook Salmon Density Revealed during the Annual Yukon River Spawning Migration, Zuray, Kocan, Hershberger 2012. Transaction of American Fisheries Society
Diagnostic Methodology is Critical for Accurately Determining the
Prevalence of Ichthyophonus Infections in Wild Fish Populations
Kocan, Dolan, Hershberger. Journal of Parasitology, 2011.
Yearly king salmon data sets from 2004 to 2010 (weights,
lengths, sex and Ichthyophonus disease rate) taken in the subsistence/commercial fishery
at Rampart Rapids, Rapids Research Center
Chinook Salmon Ichthyophonus Investigations, Larissa Dehn, Krista Nichols, Christopher Whipps, 2010
Effects of temperature on disease progression and
swimming stamina in Ichthyophonus-infected rainbow trout, 2009
Kocan, Hershberger, Sanders, and Winton
Evidence that PCR Diagnostics Underestimate Infection Prevalence
of Ichthyophonus in Yukon River Chinook salmon, 2009. R.M. Kocan, Ph.D.
Professor Emeritus, School of Aquatic & Fishery Sciences, University of Washington
Potential for cross-contamination of in vitro explant cultures initiated from
Ichthyophonus-infected rainbow trout, Oncorhynchus mykiss (Walbaum)
S LaPatra, R Kocan and P Hershberger
Ichthyophonus-induced cardiac damage: a mechanism for reduced swimming stamina in salmonids, R Kocan, S LaPatra, J Gregg, J Winton and P Hershberger, Journal of Fish Diseases 2006, 29, 521-527
2007 Rapids Student Data Collection - Raw Data Report.xls
Assessment of Ichthyophonus in Chinook salmon within the Yukon River Drainage 2004, Alaska Department of Fish and Game, Fishery Data series No. 07-64
Review of ADF&G Fishery Data series No. 07-64 by Dr Richard Kocan
2006 Rapids Student Data Collection Project Report (multiple graphs, tables and pictures related to Ichthyophonus on the Yukon River)
Differences in Ichthyophonus prevalence and infection severity between upper Yukon River and Tanana River chinook salmon, Oncorhynchus tshawytscha (Walbaum), stocks
R Kocan and P Hershberger, Journal of Fish Diseases 2006, 29, 497-503
Ichthyophonaisis: An Emerging Disease of Chinook Salmon in the Yukon River, Journal of Aquatic Animal Health, 2004, Kocan, Hershberger, Winton
Ichthyophonus Pilot Project - Yukon River King Salmon - Final Report for 2000, R. M. Kocan Ph. D. and P. K. Hershberger Ph. D
Effects of Ichthyophonus on Survival and Reproductive Success of Yukon River Chinook Salmon, 2001 - Kocan, Hershberger and Winton
Appendix I - Summary of infection and disease prevalence in Yukon and Tanana River, 1999 - 2002, Kocan, Hershberger, Winton
Appendix II - Gross tissue lesions caused by Ichthyophonus sp.
Kocan, Hershberger, Winton
Appendix III - In vitro culture of Ichthyophonus from infected fish tissues,
Kocan, Hershberger and Winton
Appendix IV - Miscellaneous abnormalities observed in Yukon River fish between 1999 & 2002, Kocan, Hershberger, Winton
Yukon River/Bering Sea Ichthyophonus Scoping and Planning Meeting Notes, October 13 - 14, 2004
Alaska Dept. of Fish and Game 2005 Ichthyophonus Presentation
to the Yukon River Panel. (Powerpoint)
General Responses to 2005 Yukon River Chinook Salmon Ichthyophonus Update presented to the Yukon River Panel on December 7-8 2005,
by DR. Richard Kocan on January 28, 2006
Comments on 2005 ADF&G Chinook Salmon Ichthyophonus Update Presentation to the Yukon River Panel, Comments by Simon Jones, Fisheries and Oceans, Canada, Pacific Biological Station, Nanaimo, BC, 2006