Spots and Fish Diseases

Even if you don’t hunt or fish, if you spend enough time outdoors you’re bound to come across something a little out of the ordinary – perhaps a deer with an odd growth, a raccoon acting strangely or even a bird with a peculiar coloration.

Game and Fish biologists get a fair number of calls, emails and questions on these outdoors oddities, and I enjoy the discussions that accompany the reports.

After asking for a description (a picture is always preferred) and explanation of the surroundings, climate conditions and any other pertinent information, I always want to know if the observance was isolated, or if there were other fish, deer or fowl in the area with similar behaviors or appearances.

In all circumstances, if it’s a single, unique event I explain how wildlife and fish are susceptible to injury, disease and genetic issues, just as are humans.

While most of the calls relate to wildlife, some involve fish, as several types of diseases are occasionally seen in North Dakota fish.

If you catch a fish that looks like it has warts, it’s probably infected with Lymphocystis or “fish warts.” This is one of the more commonly reported viral diseases in fish.

If you catch a fish with other types of bacterial skin infection, the flesh of the fish should be edible when cleaned, prepared and cooked properly.

A fungal infection may appear as gray-white mats on the skin. Fungal infections can occur when fish are stressed or injured, especially when their slime coating is damaged. The fungus can progress to the point where it covers, and eventually kills, the fish.

Since the mucous (slime coat) is a fish’s first defense against fungal or bacterial infections, anglers should take special care to not damage any fish you plan to release.

If you harvest a fish with a fungal infection, the flesh should be edible if cleaned, prepared and cooked as usual.

In walleye, sandy flesh (myofi brogranuloma) is a form of muscle degeneration often compared to muscular dystrophy in humans, because it has similar symptoms. An affected fish shows no external symptoms or abnormal behavior. However, the fillets will have a rough, sandy texture that resembles freezer burn. The flesh may range from slightly discolored to yellowish-brown.

Although there is no known link between fish and muscular dystrophy in humans, the cause of sandy flesh is not known and it’s recommended that you do not eat an infected fish.

North Dakota has a few other fish diseases or abnormalities than those discussed above. If you catch something that has an odd growth or appearance, call Game and Fish or email in a photo.

And if you’re not comfortable with the look or taste of the fish if you do fry it up, personally, if it doesn’t look right or tastes a bit funny, I’d rather be safe than sorry.

Doug Leier is a biologist for the Game and Fish Department. He can be reached via email: dleier@nd.gov

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