Cover photos credit: Photo Field Guide to the Freshwater Mussels of Ontario



“Endangered” means the species lives in the wild in Ontario but is facing imminent extinction or extirpation.

Date added to the Species at Risk in Ontario List

The Round pigtoe was already assessed as Endangered when the Endangered Species Act took effect in 2008. It was re-assessed as endangered in 2014.

Read the report (PDF)

What it looks like

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.

Where it lives

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.

Where it’s been found in Ontario

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.

map of round pigtoe range

View a Larger version of this map (PDF)

What threatens it

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.

Action we are taking

Endangered Species and their general habitat are automatically protected.

Recovery strategy

A recovery strategy advises the ministry on ways to ensure healthy numbers of the species return to Ontario.

Read the executive summary (September 10, 2010)

Read the recovery strategy (September 10, 2010)

Government response statement

A government response statement outlines the actions the government intends to take or support to help recover the species.

Read the government response statement (June 15, 2011)

Five-Year Review of Progress

A five-year review reports on progress made toward protecting and recovering a species, within five years of publishing a species’ government response statement.

Read the report on progress towards the protection and recovery of 27 species at risk, including Round Pigtoe (2016).

Habitat protection

General Habitat Protection - June 30, 2013

What you can do

Report a sighting

Report a sighting of an endangered animal or plant to the Natural Heritage Information Centre. Photographs with specific locations or mapping coordinates are always helpful.


Volunteer with your local nature club or provincial park to participate in surveys or stewardship work focused on species at risk.

Be a good steward

  • private land owners have a very important role to play in species 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:
  • farmers and land owners can help improve mussel habitat and keep Ontario’s water safe and clean by maintaining natural vegetation next to creeks and rivers, and keeping pollution and soil from washing into Ontario’s streams and rivers; for more information about programs and funding assistance for eligible land owners visit the Ontario Soil and Crop Improvement Association website

Report illegal activity

Report any illegal activity related to plants and wildlife to 1-877-TIP-SMNR (847-7667).

Quick facts

  • 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
  • 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