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Piscirickettsia

Background

In 2001 Michigan DNR Fisheries Research Biologist Mike Thomas first noticed unusual lesions on some Lake St. Clair muskies caught in fish survey traps. Affected fish were examined at Michigan State University and a positive identification of the cause was made. The disease is caused by a bacterium resembling Piscirickettsia Salmonis.

Piscirickettsia Salmonis has previously been reported only in salmonoid species. It has occurred in high-density fish populations including commercially raised salmon in Chile. The disease outbreak in Lake St. Clair is being attributed to a Piscirickettsia-like organism and it is the only confirmed case of the disease affecting muskellunge. The mortality in muskellunge is not presently known, however in the commercially raised salmon the mortality was high.

Earlier this year reports began to come in of large numbers of dead muskies seen in the Detroit River. While it isn't unusual to occasionally see some dead fish of various species, the number of dead muskies this year was considerably more than usual. Strangely enough, most if not all of the dead muskies were over 36 inches long. Based on information from people who have many years of experience with early season walleye fishing in the Detroit River, this was truly an unusual occurance. Mike Thomas did examine some of the dead muskies but they had been dead for some time and they were in bad condition and the cause of death could not be positively determined.

The disease appears as sores up to approximately one inch in size. The sores could be confused with lamprey wounds or scars, but there are differences. Lamprey wounds or scars are generally round or show a track with rounded ends, but the disease sores are sometimes irregular shaped. The disease sores are often raised whereas lamprey wounds are depressed. Additionally, the disease sores may also appear in various sizes on the same fish. Comparative pictures are shown below.

You Can Help

The DNR is taking this problem very seriously and is asking for help from the public. Volunteer anglers are needed to help with sampling during four designated "Muskie Fishing Days" on Lake St. Clair. You will need to go catch some muskies for the DNR. It's a grim job but somebody has to do it! Click here for more information.

Next, if you find a dead muskie that is in good condition, please look at it carefully to see if you can determine the cause of death. If it has gill damage from being previously caught, cuts from propeller blades, or similar injuries it's of no interest. However, if it has sores like in the pictures below, and no other apparent problems, then take a lot of pictures if you can. You can email the pictures to Mike Thomas. Include details of the fish like where found, when, and fish length. NOTE - No exception to fish size or possession limits are implied. Rocketman did NOT tell you it's OK to have undersize fish or too many of them in your boat.

It is not known if this disease is affecting populations of muskies anywhere else besides Lake St. Clair. If you find an affected fish elsewhere I suggest you contact your local DNR or MNR immediately. You will have a lot more credibility if you have some good pictures and know what you are talking about. Something detailed like "Here are pictures of a 43" Great Lakes Muskellunge that I caught in Clam Lake on May 29, 2003 and it had lesions that appear similar to those caused by the Piscirickettsia-like pathogen known to be infecting muskellunge in Lake St. Clair" sounds pretty impressive.

It is not known how this disease spreads. If your favorite TX Dog Turd catches a diseased muskie could it transmit the disease to infect the next fish? If you net an affected fish will your net be contaminated? If you trailer your boat is it possible that you could spread this disease to another body of water? Right now there are no official recommendations. Some good common sense would be to rinse off your lures, nets, hands, etc after each fish. If you trailer your boat then pull the drain plug, empty the live well, and remove any weeds from the trailer when you're done fishing. It wouldn't hurt to spray that sucker off at the car wash either before you go put it in a different lake. If anyone else has any reasonable recommendations them I would like to hear them. By the way, washing everything with a solution of 50% bleach after every fish is not reasonable.

Please do not deluge Mike Thomas with a bunch of irrelevant BS. There are lots of you and only one of him - and he's got some serious work to do. If you have something useful then send it to him but right now he's really not interested in hearing about that big sheepshead you caught in Lake Erie last summer.

Pictures

Muskie disease
several disease sores
Muskie disease
single disease sore
Muskie disease
close-up view
Lamprey wound
lamprey wound
Lamprey wound
close-up view
Lamprey scar
lamprey scar

Additional Information





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