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Q & A
Tumors on Walleye
Question
I've caught a bunch of walleye this year with unsightly growths or tumors on them. What causes these growths? Are the fish safe to eat? How should I prepare my catch?
Answer
Walleye are commonly affected by two skin conditions that may occur separately or in combination. Differentiation of the two infections may be somewhat difficult for the untrained eye. Both of these conditions are considered to be caused by fish viruses.

Walleye - click for more informationThese viral skin infections are not associated with walleye mortality, and they are harmless to humans. Infected walleye should be processed for consumption in the normal manner. On the rare occasion when a skin lesion penetrates into the musculature, that portion of the fish tissue can be removed and discarded to improve its appearance. A more detailed discussion of these two conditions is presented below.

The first condition, called lymphocystis, is commonly found in the central portion of the United States, especially in and around the Great Lakes region, and in the south-central and south-eastern regions of Canada. It is characterized by raised, rough, nodular masses of generally light colored, somewhat opalescent white, gray or cream-colored tissues that superficially resemble warts. Larger, more developed lesions may have areas of pinkish or reddish coloration due to blood vessels in the infected tissues. These lesions are usually external, located on the skin or the fins, but occasionally they are found internally along the gut and in the heart and other internal organs. Massive replication of the virus within the walleye skin cell causes the size of the infected cell to increase in size dramatically. Eventually these cells burst or slough off, releasing the virus and leaving a light colored scar. Lymphocystis usually appears in the spring and reaches maximum development in the summer. In the fall and winter the lesions gradually disappear. Although walleye are most susceptible to the lymphocystis virus, perches, sauger, darters, sunfishes, basses, bluegill and crappie can also develop the infection.

The second condition is called dermal sarcoma. This benign skin tumor is similar to lymphocystis in gross appearance and location on the fish, although dermal sarcoma tend to be found more frequently on the body than on the fins, and the lesion tends to be more variable in color, depending on the blood supply and the amount of fibrous tissue present. These single or multiple, smooth and firm nodules develop to about a half inch in diameter. They are more prevalent in the fall and spring. They are less frequently observed in the summer. Female and younger walleye tend to be more affected by this condition. The cause of dermal sarcoma has not been determined definitively, but transmission studies suggests viral activity.

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