Q: What is the cause of these sores on walleye? Is it harmful or contagious? Is the fish safe to eat?Matt Klymenko, Woods BayWatch
A: Members of the Canadian Animal Health Surveillance System’s Aquatic Network had this to say: It is likely dermal sarcoma virus, which is often confused with a lookalike fish disease, lymphocystis. Dermal sarcoma has irregularly shaped but normal-sized cells, while lymphocystis tumours have obvious enlarged cells. We can’t compare cell sizes here, but other clues can help narrow down the disease.
Peak months for lymphocystis are April and May while dermal sarcoma is less seasonal. This fish was caught and released in mid-June. One Canadian study investigated various tumours in the late 1970s that were thought to be lymphocystis, but most of them were in fact dermal sarcomas.
Dermal sarcoma and lymphocystis are distinctly different diseases, but they look very similar, exhibiting warty looking growths on the skin, fins, and other areas. They can be cream or fleshy coloured but also pinkish or red depending on abrasions or hemorrhaging. After infection, the cells grow and will eventually rupture, releasing the virus back into the water, and the lesions will become scarred over.
Most agree that dermal sarcoma isn’t particularly harmful unless it’s impeding normal functioning or the lesions become infected/ulcerated. The province recommends not eating diseased, dying, or dead fish. Although humans can’t contract these diseases from fish, it’s best to release them.
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Originally published in the Nov.-Dec. 2024 issue of Ontario OUT of DOORS
