New fish parasite spreads to walleye, northern pike

A fish parasite first discovered in yellow perch has begun to show up in other species. Officials with the Minnesota Department of Natural Resources said the parasite, called Hetersporis, has been confirmed from five lakes and reported from 25 lakes, mainly in yellow perch but also in one walleye and one northern pike. The parasite was discovered in 1999 in Minnesota's Leech Lake and Wisconsin's Eagle Chain of Lakes. The microscopic organism turns the fish filet an opaque white and can only be seen when the fish is fileted. A healthy filet is transluscent. Because the parasite is so new, officials can't ...

May 23rd 2001

A fish parasite first discovered in yellow perch has begun to show up in other species. Officials with the Minnesota Department of Natural Resources said the parasite, called Hetersporis, has been confirmed from five lakes and reported from 25 lakes, mainly in yellow perch but also in one walleye and one northern pike.

The parasite was discovered in 1999 in Minnesota’s Leech Lake and Wisconsin’s Eagle Chain of Lakes. The microscopic organism turns the fish filet an opaque white and can only be seen when the fish is fileted. A healthy filet is transluscent.

Because the parasite is so new, officials can’t yet say whether it’s dangerous to fish or aquatic ecosystems. Health officials at the Centers for Disease Control in Atlanta, Ga., said the parasite poses no risk to human health.

The parasite looks similar to harmless parasites commonly found in perch and other fish species, said Joe Marcino, who manages the Minnesota DNR pathology laboratory. However, it appears to be of the genus Hetersporis, a parasite that had only been reported in fish from Germany, France, Japan and Taiwan. The parasite was not known to ever be in North American waters before 1999. It is not known if the parasite is an exotic species or is native to North America and has only recently been discovered.

Marcino said he does not know if the increased number of lakes with fish having the parasite indicates that the organism is spreading or simply reflects increased reporting by anglers.

The parasite is killed when the meat is cooked thoroughly.

To prevent the parasite from spreading, Wisconsin health officials recommend that infected fish or filets be disposed of in the garbage or buried, but not thrown back into the lake. Marcino said that anglers should drain water from the motor, livewell, bilge and transom wells at the boat ramp before leaving any lake. Anglers should dispose of any unwanted minnows and leeches — and the water they are in — on shore.

“Basically, anglers should follow the same procedures the DNR recommends for stopping the spread of any aquatic exotic species,” Marcino said.

So that he can learn more about the range of the parasite in Minnesota, Marcino is urging anglers to call or send e-mail to him if filets of perch, walleye, sauger or northern pike have opaque white portions. He can be reached at (651) 296-3043 or joe.marcino@dnr.state.mn.us.

Lakes where fish containing the parasite have been reported are Lake Mille Lacs in Isanti County; Lake Vermillion in St. Louis County; Leech Lake in Cass County; Andrusia Lake in Beltrami Count;, and Horsehead and Clitheral lakes in Otter Tail County.