Species At Risk

Round Pigtoe

(Pleurobema sintoxia)


Round Pigtoe
Round Pigtoe occurrences map


The Round Pigtoe 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 look like the growth rings in a tree stump.


In Canada, Round Pigtoe are found only in southwestern Ontario, mainly in the St. Clair River delta and the Sydenham River but small populations still exist in the Grand and Thames rivers and in shallow areas near the shorelines of Lake Erie and Lake St. Clair.


The Round Pigtoe is usually found in rivers of various sizes with deep water and sandy, rocky, or mud bottoms. Like all freshwater mussels, this species feeds on algae and bacteria that it filters out of the water. Mussel larvae are parasitic and must attach to a fish host, where they consume nutrients from the fish body until they transform into juvenile mussels and drop off. Known fish hosts of the Round Pigtoe include: Bluegill, Spotfin Shiner, Bluntnose Minnow, and Northern Redbelly Dace. The presence of fish hosts is one of the key features for an area to support a healthy mussel population.


The greatest threats to the Round Pigtoe are invasive species, pollution from agriculture and siltation, which occurs when too much soil washes into the river from nearby agricultural and urban areas. The Zebra Mussel, an invasive species from Europe, is a serious concern because it attaches to native mussels and can interfere with breathing, feeding, excretion and movement. Conditions that threaten the fish host species can also threaten the Round Pigtoe.


The Round Pigtoe is protected under Ontario’s Endangered Species Act and the federal Species at Risk Act.

What You Can Do to Help the Round Pigtoe

  • The Ministry of Natural Resources tracks species at risk such as the Round Pigtoe. You can use a handy online form to report your sightings to the Natural Heritage Information Centre. Photographs with specific locations or mapping coordinates are always helpful. nhic.mnr.gov.on.ca
  • Report any illegal activity related to plants and wildlife to 1-877-TIPS-MNR (847-7667).
  • You can help improve mussel habitat and keep Ontario’s water safe and clean by maintaining natural vegetation next to creeks and rivers. The roots of 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. There are many other things that you can do to help reduce soil erosion and you might be eligible for funding assistance. For more information, visit the Ontario Soil and Crop Improvement Association: www.ontariosoilcrop.org.
  • Private land owners have a very important role to play in species at risk recovery. If you find Round Pigtoe in a watercourse on or adjacent to your property, you may be eligible for stewardship programs that support the protection and recovery of species at risk and their habitats.
  • Invasive species seriously threaten many of Ontario’s species at risk. To learn what you can do to help reduce the threat of invasive species, visit: ontario.ca/invasivespecies ; www.invadingspecies.com ; www.ontarioinvasiveplants.ca ; and, www.invasivespecies.gc.ca .
  • Volunteer with your local nature club or provincial park to participate in surveys or stewardship work focused on species at risk.

Did you know?

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.

Did you know?

Mussel larvae have a very low survival rate, so mussels will produce a lot of larvae - often over a million!

Did you know?

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.

Did you know?

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.

Did you know?

Aboriginal people harvested mussels for food and to create jewelry and tools. In the 1800s, massive numbers of mussels were harvested from the Grand River to create buttons. Millions were shipped out every year until the 1940s when plastic became more common.

The Endangered Species Act

Contact your local ministry office

Often the best source of local information on species at risk is your nearest ministry office. Call with your questions or concerns.