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In the lower Yukon the disease usually has only begun. 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 prevalence can now be accurately looked at (these run roughly 25%). 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 present day lack of the older Chinook age classes (see graph below - YRDFA funded study). 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
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
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 2005 example below) is very important to do consistent, yearly, full season disease monitoring, and infection rate 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.
So how accurate is Ichthyophonus monitoring (which produced the above data) using visual techniques and student technicians. In 2006 the Student Data Collection Project funded by YRDFA was able to have DR. Kocan do a laboratory assessment of a small sampling of Chinook hearts that were visually diagnosed as positive. The results below:
2006 Examination of Histology Slides of Rapids Data Collection Project Samples, Dr Richard Kocan School of Aquatic & Fishery Sciences, University of Washington, Seattle, WA
I just finished examining the histology slides we made from the 12 Chinook samples you sent. We got both H&E and PAS stains to be certain that we didn't miss any positives. I examined 10 microscopic fields at 10X magnification and calculated the mean number of spores per 10X field for each fish. This gives the very minimum number of ICH positives, but in this case it didn't matter.
Results:
1. Tissues from 12 fish examined (10 fields at 10X magnification)
2. 12/12 (100%) were positive for Ichthyophonus
3. 9 were heavily infected (5-20+ spores per 10X field)
4. 3 were lightly infected (< 1 spore per 10 X field)
Seven of the 9 heavily infected fish had a preponderance of large spores (>100 microns) indicating a "mature" or long standing infection. Two of the 9 had a preponderance of small spores, which suggests they have less mature infections or that they were more recently infected than those with the large spores.
Based on these results your evaluation of "clinical infections" in Chinook at the Rapids is essentially 100% correct. This is supported by our earlier studies where 98% of ALL clinical diagnoses were verified by culturing the same tissue.
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
 Just Out 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
 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
 2005 Yukon River Chinook Salmon Ichthyophonus Update Presentation to the Yukon River Panel, December 7-8, 2005, Comments by Simon Jones, Fisheries and Oceans, Canada, Pacific Biological Station, Nanaimo, BC, 2006
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