Species At Risk

Round Hickorynut

(Obovaria subrotunda)


Round Hickorynut
Round Hickorynut occurrences map


The Round Hickorynut is a small to medium freshwater mussel that can reach up to 6.5 centimetres long. It is easily distinguished from other Ontario mussels by its almost perfectly round shape. The shell is thick, solid, and dark chocolate brown in colour, with a distinctly lighter coloured band along one side.


The Round Hickorynut has been lost from 90 per cent of its former range in Canada. It is now found only in the Sydenham River and the St. Clair River delta in Lake St. Clair in southwest Ontario. Populations have been lost from the rest of Lake St. Clair, the Thames River, the Detroit River, Lake Erie and the Grand and Niagara River drainages.


In Ontario, the Round Hickorynut is mainly found in rivers with clay, sand, or gravel bottoms. It also lives in shallow areas of lakes with firm sand. It prefers moderately fast moving water. Like all mussels, this species filters water to find food, such as bacteria and algae. 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. The fish hosts of the Round Hickorynut in Canada have not been confirmed but may include the Greenside Darter and the Eastern Sand Darter, which is also a species at risk. 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 Hickorynut are pollution 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 threat because it attaches to native mussels and can kill them by interfering with breathing, feeding, excretion and movement. Conditions that threaten the fish host species also threaten the Round Hickorynut.


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

What You Can Do to Help the Round Hickorynut

  • The Ministry of Natural Resources tracks species at risk such as the Round Hickorynut. 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 Hickorynut 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?

It is estimated that Round Hickorynut populations in Canada have declined by more than 90 per cent since the invasion of the Great Lakes by Zebra Mussels.

Did you know?

Mussels are indicators of environmental health. Since they have a complex life cycle, are long-lived and feed 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 buttons became more popular.

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.