Cause of disease:

Heterosporis Parasite

What does it look like?

White or "opaque areas" in the uncooked fish fillet. White regions on the fillet that resemble cooked meat.



Fish species affected:

Predominantly seen in yellow perch, this disease has also been detected in walleye, northern pike, trout-perch, burbot, pumpkinseed, sculpin and rock bass.

Life cycle:

Heterosporis spreads when fish pick up spores from the water or eat infected fish or carcasses. Little is known about the life cycle. This parasite may spread by infected fathead minnows sold as bait.

Where is the disease is found?

Heterosporis infections in Minnesota have been documented in Big Sand, Winnibigoshish, Leech, Clitherall, Vermilion, Mille Lacs, Bear, Moose, Cass, Andrusia, and Gull lakes. The disease is also found in Canada.

Is it safe to eat?

Based on studies by the Center for Disease Control in Atlanta, there is no evidence that heterosporis can infect people. It is thought, but not proven; that thoroughly cooking infected fish will destroy spores. Either cook the fish thoroughly or discard the flesh by burning or burying it. Don't throw it back into the lake.

How can I prevent the spread?

To reduce the risk of spreading heterosporis, never release unused minnows into lakes. If you see opaque-looking patches when you fillet a fish, report it to the DNR by calling (888) 646-6367.

Effects on fish:

Heterosporis is a microscopic parasite that infects muscle tissue of fish. These parasites produce millions of spores, which gradually destroy muscle tissue. These spores can eventually replace almost all muscle tissue.

Disposal of unused portions:

Unused or uneaten portions of fish should be buried or disposed of with household waste. Fish entrails should never be discarded back into the lake.

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