Canadian freshwater mussels and their host associations

Freshwater mussels (order Unionida) are one of the world’s most imperiled taxonomic groups of animals. The two families that occur in Canada (Margaritiferidae, Unionidae) produce parasitic larvae (glochidia) that generally rely on attachment to a suitable host fish to facilitate metamorphosis into the juvenile phase. This review synthesizes the current knowledge on the hosts of all 55 species of freshwater mussels in Canada, compiled from 265 citations, 71 of which were newly identified by this review. As of October 2023, evidence for 850 mussel–host associations have been documented, though a relatively small proportion of the evidence was collected in Canada. The winged floater and the lake floater currently have no known hosts, with 14 other species having only a single associated evidence type. This review provides an updated library of current knowledge on hosts of Canadian unionoids, discusses notable trends, and outlines outstanding knowledge gaps to be addressed in future studies. Considering many of the host associations were not studied in Canadian waters, knowledge gaps remain regarding relevant ecological and climatic context in Canada.