Muskie Pox (Piscirickettsia)

Piscirickettsia - A New Pathogen in Lake St. Clair Muskies - A Fact Sheet of our Current Knowledge

Resource Background: The muskellunge fishery of Lake St. Clair has a reputation among muskie anglers for unusually high catch rates. The fishery draws anglers from the local area as well as from across the continent. Numerous charter fishing businesses specialize in muskie trips. Countless individual anglers fish exclusively for muskellunge while the season is open. A large Detroit area angling club is dedicated to the sport of muskie fishing. Many Lake St. Clair muskellunge anglers espouse a strict catch-and-release ethic. The Lake St. Clair muskellunge fishery is completely self-sustaining, thus any threat to the continued successful recruitment of muskellunge in the lake is a serious concern for fisheries managers.

Pathogen Detection in Lake St. Clair: : In May of 2002, the Michigan Department of Natural Resources (MDNR) collected several muskellunge exhibiting unusual red skin rashes from the Anchor Bay area of Lake St. Clair. The rounded rashes reached up to one inch in diameter (Figure 1). Laboratory analysis at Michigan State University by Dr. Mohamed Faisal, revealed the association of these lesions with a Gram-negative, curved, intracellular bacterium that occurred as rings or curved rods (Figure 2). Based on their shape and culture characteristics, the organism was determined to be a Piscirickettsia-like organism.

Pathogen Facts:

  • Piscirickettsia salmonis (P. salmonis ) was the first "rickettsia-like" bacteria to be recognized as a pathogenic agent of fish.
  • P. salmonis infects a wide range of salmonid fish species causing a systemic infection associated with high mortalities in Chile, Norway, Ireland, and Canada. This organism has never been found in any non-salmonid fish species.
  • Similar agents, known as Piscirickettsia-like organisms, have been found to be associated with increased mortality rates in diverse fish species, including white seabass, black seabass, tilapia, blue-eyed plecostomus, and dragonet. Three of these Piscirickettsia-like organisms have already been reported in non-salmonid fish species in North America.
  • Piscirickettsia are not known to infect human or other terrestrial animals.

Pathogen Impacts in Lake St. Clair: While the Piscirickettsia-like organism has been found in Lake St. Clair, DNR surveys and reports by fishermen have not indicated negative impacts in the muskellunge fishery.

Fisheries Division Action Plan: The discovery of this infection in Lake St. Clair muskellunge has raised the following questions:


  • How widespread is the disease in the lake's muskellunge population?
  • Does the organism affect the longevity of infected fish?
  • What could be the source of the infection?
  • What measures should be undertaken to prevent the spread of this infection?
  • Are other fish species affected?
  • Will the infection affect the abundance of muskellunge in the lake?

In response to public concerns, the DNR has assembled a team of fishery biologists, managers, and specialized veterinarians that continue to monitor this case. Muskie anglers wishing to assist in this effort and anglers that catch a muskie in Lake St. Clair bearing red sores similar to those shown below are asked to report their observation to the Lake St. Clair Fisheries Research Station using the following contact information.

For more information on Piscirickettsia in Lake St. Clair's muskellunge:

Todd Wills, Area Research Manager
Lake St. Clair Fisheries Research Station
Tel: 586-465-4771 ext. 22

Gary Whelan, Program Manager
MDNR Fisheries Division Research Section
Tel: 517-284-5840


Muskellunge with lesions
Figure 1. A Lake St. Clair muskellunge bearing the red lesions or sores characteristic of the Piscirickettsia infection.


Muskellunge bacterium
Figure 2. Electron microscopy image of the Piscirickettsia sp. bacterium isolated from Lake St. Clair muskellunge in 2002.