This Week’s Endangered Species in Focus: Round Pigtoe (Pleurobema sintoxia)



The Round Pigtoe is one of Canada’s 54 freshwater mussel species, it is a medium to large-sized freshwater mussel that may reach 13 centimetres in length. Adults have a thick, solid, mahogany-coloured shell with dark bands. Juvenile shells are tan with green lines. This species develops growth rings as it ages, which resemble those of a tree stump.


Status: Endangered Provincially and Nationally


Important Dates:

June 30, 2008: Species listed at Risk

June 30, 2013: Species granted Habitat Protection



  • In Ontario, it is found in the Grand, Thames and Sydenham rivers, found around Walpole Island in Lake St. Clair, and shallow areas along the shorelines of Lake Erie.



  • Lives in a wide range of habitats, from small rivers in area of moderate flow with gravel, cobble and boulder bottoms, to larger rivers in mud, sand and gravel at varying depths;
  • Its breeding season lasts from early May to late July and the larvae are released before winter;
  • Like all freshwater mussels, this species feeds on algae and bacteria that it filters out of the water;
  • Mussel larvae are parasitic (an animal or plant that lives in or on another (the host) from which it obtains nourishment) and must attach to a fish host – some known hosts are Bluegill, Spotfin Shiner and Bluntnose Minnow



  • Introduction and spread of the Zebra Mussel throughout the Great Lakes severely reduced or eliminated the Round Pigtoe in Lake St. Clair, Lake Erie and the Detroit and Niagara rivers;
  • Decreased water quality from pollution continue to threaten the round pigtoe



  • Under the Ontario Endangered Species Act, the Round Pigtoe is protected against threat of being killed, collected, possessed, sold or traded;
  • Under SARA (Species at Risk Act), a recovery strategy and an action plan have been developed to prevent the loss and maintain/return healthy self-sustaining populations of the Round Pigtoe


What You Can Do To Help:

  • Help improve mussel habitat by maintaining natural vegetation next to creeks and rivers. The roots of the plants reduce erosion and can stop soil from washing into the river;
  • Fence off streamside areas to keep cattle (and their manure) out of the water;
  • Volunteer with your local nature club or provincial park to participate in surveys or stewardship work focused on species at risk



  • Round Pigtoe eggs hatch inside a special pouch in the mother’s gills called a marsupium, where the larvae are supported before being ejected into the water;
  • Mussel larvae have a very low survival rate, so mussels will produce a lot of larvae – often over a million;
  • Mussels rely on a lot of good luck in order to reproduce. Males release sperm into the water, and if there happens to be a female nearby, she will capture the sperm as she filters water for food;
  • Mussels are indicators of environmental health. Since they have a complex life cycle, are long-lived species (some can live up to 100 years!), and eat by filtering water and its pollutants, mussels can provide a snapshot of how healthy our waterways are.


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