Infectious Diseases of Freshwater Mussels and Other Freshwater Bivalve Mollusks

Numerous species of freshwater mussels (order Unionoida) are imperiled in the wild, and unionoids and other freshwater bivalves are important components of many ecosystems. Freshwater mussels also are propagated in captivity for production of pearls and enhancement of wild populations. However, infectious diseases of these mollusks have received relatively little attention. Unionidae is the most diverse family of freshwater bivalves, and most of the information available for this review is about species in this family. Eukaryotic organisms, especially trematodes, mites, and Conchophthirus spp. (Ciliata) are common inhabitants of unionids, and some have the potential to decrease the fitness of the host unionid. Several species of potentially pathogenic bacteria have been isolated from freshwater bivalves, but their role in diseases of bivalves has not been established. Evidence for viral diseases has been found in only one species of freshwater bivalve, a Chinese pearl mussel, Hyriopsis cumingii. The potential for some pathogens to cause greater harm to freshwater bivalves during periods of suboptimal conditions has not been evaluated adequately. Additional research is also needed to determine whether other types of pathogens are present in freshwater bivalves.