Walleye with Lymphocytes

A growth on a walleye pulled from Mille Lacs Lake a couple weeks ago grabbed the attention, and perplexed, users of social media.

The abnormality looks to be Lymphocystis, said Rebecca Munter, assistant area supervisor for the DNR’s Fish and Wildlife Division. “Lymphocystis is a virus that infects the skin of a fish, and in Minnesota, it is most commonly observed in adult walleye,” said Munter. “We observe it every year in our fall gill net sampling in maybe 5 percent of the fish that we handle, it is not an unusual abnormality for walleye in Mille Lacs.”

Munter said the virus spreads from fish to fish via either skin to skin contact or through the water. These walleye can be consumed with proper cooking guidelines as is recommended with any freshwater fish, she added. This disease is not known to infect humans.

The DNR website describes the symptoms as “warts” or tumors that are commonly seen on the skin and/or fins of adult fish. The abnormality has been documented throughout the world on many species of freshwater and marine fishes, but in Minnesota, it is most commonly observed on adult walleye.

Lymphocystis infections are usually not fatal to fish, says the DNR, although very severe infections can cause damage to vital organs and possibly death. In addition, secondary bacterial or fungal infections can develop at sites of dislodged growths. There is no practical control or treatment for this disease.

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