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Warmer Water Means More Parasites In Kuskokwim Salmon

Warmer ocean and river water has increased the number of the parasites ichthyophonus and henneguya in Kuskokwim salmon  during the 2019 fishing season.
Avery Hoffman

Subsistence families along the Kuskokwim River are cutting open fish to find white balls or white streaks deforming the meat. The marks are formed from the parasites ichthyophonus and henneguya, also known as tapioca disease. Subsistence users are familiar with these parasites, but Alaska Department of Fish and Game biologist Aaron Tiernan says his office has never received as many reports of the diseases as they have this season. He attributes the extreme growth to warm water in the Bering Sea and Kuskokwim River.

Tiernan assures users that meat infected with these parasites are safe to eat after being properly frozen or cooked, even if it doesn’t look appetizing. 

KYUK talked with Tiernan more about this infestation.


KYUK: What do these two diseases look like? If you were to slice open a fish, what would you see?

Tiernan: Ichthyophonus can provide almost like this white marbling on the salmon flesh. Little patches of white throughout the whole filet. Sometimes it's more of an opaque white or a kind of a dull white. You can see other forms of it in the kidney of the salmon, that blood line that runs right underneath the spinal column within the belly cavity. It almost looks like granular grains of sand in there. Henneguya, or tapioca disease, is like little white pus pockets within the fish. 

It appears that both of them are parasites. I believe that they can contract them both in the fresh and the saltwater environments. They can get them from food that they're eating, whether as they're youngsters or they're growing out in the ocean becoming more mature. It's nothing new to salmon. We've seen it, but it just seems like when we're dealing with a little bit warmer water conditions in river and out in the ocean, that it presents itself within the flesh a little bit more. 

KYUK: How much warmer is the water both in the ocean and in the river?

Tiernan: Based on what I looked in Kuskokwim Bay, we're looking at approximately 5.5 degree Celsius increase from normal temperatures right now. In [the Kuskokwim] River we are probably three or four degrees warmer than our historical average at the Bethel Test Fish site. We're not well outside the range that we've seen at Bethel Test Fish, but we're definitely at the upper end of that range of temperatures we've seen on this during this timeframe. 

KYUK: And why do warmer conditions increase the prevalence of these parasites?

Tiernan: We have refrigerators with our leftover food from cooking dinner. We put it in there so it'll keep a little bit longer and bacteria might not grow on it as fast. Salmon flesh,when it's in good cold water, if it's diseased, some of it might show up and you'll see it. But when things start to warm, growth rates tend to increase as well. So the parasite with a little bit warmer environment within its host can present itself at an increased rate. 

KYUK: So the salmon could be carrying the parasite in colder water, but when you harvest it, you might not see it? Whereas if it was coming up river in warmer water you would more likely see it?

Tiernan: Right. That's what we've come up with through our research after getting all of these reports. 

KYUK: Is one species showing that they carry these parasites more than another species?

Tiernan: Nope, we're getting reports of both of these parasites and all species of fish: sockeye, chum, kings. So it doesn't appear like it's a singular species is more affected than the others. 

KYUK: Aaron Tiernan is the Kusokwim Area Biologist for the Alaska Department of Fish and Game. Thank you, Aaron. 

Tiernan: Thank you. 

Aaron Tiernan has worked with the Alaska Department of Fish and Game on the Kuskokwim River since 2013. He has recently accepted a job in Bristol Bay and will begin managing a portion of the salmon run in that region.

Anna Rose MacArthur served as KYUK's News Director from 2015-2022.