
Species Identification:
The Rainbow (Villosa iris) is one of Canada’s 54 freshwater mussel species. It is a small, pretty mussel that gets its common name, “Rainbow”, from the shimmering, iridescent inside of its shell. Narrow, relatively thin, and small (average length of 2”), the shell is oval-shaped, with a rounded posterior in females, and blunt pointed posterior in males.
Diet:
Rainbow larvae, like those of most other freshwater mussels, are parasitic to fish – in The Land Between, their hosts include Smallmouth Bass, Largemouth Bass, Green Sunfish, Rainbow Darter, Yellow Perch, Mottled Sculpin and Rock Bass.
Juvenile Rainbow live completely burrowed in the substrate, where they feed on organic particles present in the substrate or interstitial water; the diet of adult Rainbow is similar, comprising of bacteria, algae and other organic particles filtered from the water column.

Biology and Behaviour:
Rainbow has separate sexes, but males and females are difficult to tell apart as they differ only slightly in shell shape. Rainbow is a long-term brooder that spawns in the late summer, broods its glochidia (larvae) over the winter and releases them in the early spring. Like most other freshwater mussels, the larvae are parasitic on fishes: they attach to the gills of a host fish until they reach their juvenile, free-living stage and drop off to burrow in the substrate below.
Sexual maturity occurs between 5 – 9 years of age and individuals can live up to 43 years. Adult Rainbow are essentially sessile and may move only a few meters along the substrate.


Conservation and recovery strategies:
Rainbow is within the range of several multi-species or ecosystem-based recovery strategies or action plans that have been drafted or completed; because the threats to this species are the same threats that affect habitats as well as other SARs, large scale conservation strategies that seek to address these threats will also support the recovery and conservation of Rainbow.
However, a single-species recovery strategy (and action plan) is best suited for Rainbow. This is because, while its range and distribution overlaps partially with other mussel species at risk in some watersheds, it also occurs in several watersheds where other species at risk mussels do not occur (e.g., Maitland, Saugeen, Salmon and Moira rivers).
Additional Resources:
Sources:
COSEWIC. 2015. COSEWIC assessment and status report on the Rainbow Villosa iris in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xii + 82 pp. (http://www.registrelep-sararegistry.gc.ca/default_e.cfm).
Fisheries and Oceans Canada. 2018. Recovery strategy and action plan for the Rainbow (Villosa iris) in Canada [Proposed]. Species at Risk Act Recovery Strategy Series. Fisheries and Oceans Canada, Ottawa. v + 63 pp.
Government of Ontario. 2016. Rainbow (Villas iris). Retrieved from: https://species-registry.canada.ca/index-en.html#/species/943-644
