Biologists from Michigan State University have identified bacteria in wounds found on Lake St. Clair muskellunge that may cause disease in the fish. To date, the Ministry of Natural Resources (MNR) has received no information that the disease has been observed in muskellunge in the Ontario waters of Lake St. Clair or elsewhere in Ontario.

In 2001 and 2002, Michigan Department of Natural Resources (DNR) biologists observed quarter-sized, rash-like lesions on live muskellunge caught in trap nets while conducting spring sampling programs on Lake St. Clair. In 2002, biologists at Michigan State University identified bacteria from the lesions on these fish as Piscirickettsia.

Piscirickettsia is a group of bacteria that may cause disease in fish under certain conditions. This group of bacteria was first identified in 1989 in young farmed salmon in Chile, and has since been found in salmon in southern California and British Columbia. The associated disease, piscirickettsiosis, has caused high mortality in farmed salmon. There is no indication that piscirickettsiosis in muskellunge is threatening to the population or causing mortality.

This is the first record of Piscirickettsia in the Great Lakes basin and the first isolation of the bacteria from muskellunge, or any other wild freshwater fish. The species of bacterium that causes the disease has not yet been identified, but it is believed to be different than that previously identified in salmon.

Reports from MNR’s 2001 fall adult muskellunge assessment program and from the summer 2002 Lake St. Clair Angler Creel Survey recorded no occurrences of lesions on muskies. The Lake St. Clair Annual Sport Diary Program reported a total sport catch of 844 muskellunge, and no anglers commented on fish with unidentified lesions.

The Ministry of Natural Resources will work with Michigan DNR to monitor the muskellunge population in Lake St. Clair for fish with lesions, as well as the incidence and prevalence of this disease in Lake St. Clair.