Features: The Rainbow Mussel (Villosa iris) is a small freshwater mussel that grows to about 5 cm long and has a compressed, elliptical shape. The shell is yellowish, yellowish-green or brown with many dark green rays. The nacre (smooth inner surface of the shell) is silvery white and iridescent, giving rise to the species’ common name. Like all unionid mussels, it is parasitic on the gills or fins of fish during their larval stage (called a glochidium). The Rainbow Mussel prefers small to medium-sized rivers, but can also be found in inland lakes. It once occurred throughout the lower Great Lakes and connecting channels. It is most numerous in clean, well-oxygenated waters at depths of less than one metre.

Status: Threatened Provincially and Nationally

Range: The Rainbow Mussel was once widely distributed in North America, ranging from New York and Ontario west to Wisconsin and south to Oklahoma, Arkansas and Alabama. In Ontario it has been found in the Ausable, Bayfield, Detroit, Grand, Maitland, Moira, Niagara, Salmon, Saugeen, Sydenham, Thames and Trent Rivers and the St. Clair river delta, as well as Lakes Huron, Ontario, and Erie. However, it has likely been lost from the rest of the lower Great Lakes and connecting channels due in large part to displacement by the exotic Zebra mussel (Dreissena polymorpha). Range Maps

Threats: Zebra mussels are a continuing threat to native freshwater mussels, particularly those in the delta. As well, heavy loadings of sediment, nutrients and toxic substances from urban and agricultural sources have degraded mussel habitat throughout southern Ontario. Studies have shown that the Rainbow Mussel is particularly sensitive to copper and ammonia.

Protection: Since June 30th, 2008, the Endangered Species Act, 2007, provides legal protection to threatened species like the Rainbow Mussel. This species may be provided with general habitat protection under the Fisheries Act, as well as Ontario's Planning Act, which addresses development in riparian areas. Collection and harvest of mussel species is controlled through the Ontario Fishery Regulations.

Text Sources: McGoldrick and Metclafe-Smith 2006

Last Modified Date: October 2008