Coho Salmon (Oncorhynchus kisutch) with Parasites

Observation: We fillet a fish and noticed that there were bumps on the fish between the skin and the flesh. Once you filleted them you could see the pus bumps inside. It was a coho salmon that we caught while sport fishing. There were a few of these pus bumps on the reds and kings but much more on the coho. One day we caught twenty of thirty salmon and one or two would be like this. I was wondering if this fish was safe to eat. People think that when you see fish like this you should not eat it and instead give it to the dogs. We are also wondering what is causing this, and why there is more now? Peter Gumlickpuk, New Stuyahok Traditional Council, IGAP Coordinator, and Moxie Andrew Jr.

Alaska Department of Fish & Game Consult: Ted Meyer, Fish Pathologist, writes, "The first photo is likely Myxobolus squamalis with cysts under the scales (Pg 48 in the ADF&G fish disease guide) while #2 is likely Henneguya salminicola (Pg 40). So two different myxosporideans. These are common parasites with prevalence’s that go up and down with no predictability. Juvenile fish are infected in freshwater as indicated in the guide text so any changes in the freshwater environment such as water temperatures, water flows, numbers of the intermediate worm hosts, numbers of infected returning fish that re-infect the worm populations, etc. can all influence the prevalence’s in the next generations of fish. It is a complex set of variables that can influence parasite prevalences which may differ from one year to the next between or among any given watersheds. The good news is that fish populations are rarely affected by these parasites which are generally benign. The bad news is that in high prevalence year’s folks have to put up with the undesirable appearance of the fish flesh which poses no human health concern."

Sea Grant Alaska, Marine Advisory Program Consult: Gabe Dunham, Map Agent writes, "Parasites are normal and can occur naturally in wild plants, fish and animals. Henneguya for example occurs most commonly in silver salmon and, is not harmful to humans. There are however, other parasites that can be present in salmon and passed on to humans. To kill parasites, freeze fish at -4 degrees Fahrenheit for 7 hours, or cook to 145 degrees Fahrenheit for 15 seconds. Retrieved from Seafood Health Facts: Making Smart Choices, for more information about Parasites, follow the link." Source: University of Alaska Fairbanks

LEO says: A good reference for learning about illness in salmon; Common Diseases of Wild and Cultured Fishes in Alaska. As residents on the Upper Nushagak are concerned about the emergence of parasites and other conditions in their fish, continued monitoring of fish and environmental conditions and research into the factors that influence fish health should be considered. Efforts to improve stream monitoring at the community level is one positive step in increasing local participation and awareness. Consultation by fisheries experts is recommended.