Vietnam has the second highest diversity of freshwater mussels (Unionida) in Asia after China. The purpose of this paper is to compile an up-to-date list of the modern unionid fauna of Vietnam and its current conservation status. Unfortunately, there has been relatively little research on this fauna in Vietnam. Fifty-nine species of Unionida have been recorded from Vietnam based on literature, museum records, and our fieldwork. Fifty were assessed in the International Union for Conservation of Nature (IUCN) Red List 2016 in the IUCN categories of Critically Endangered (four species, 6.8%), Endangered (seven species, 12%), Vulnerable (one species, 1.7%), Near Threatened (two species, 3.4%), Least Concern (23 species, 39%), Data Deficient (11 species, 18.6%), and Not Evaluated (11 species, 18.6%). Considering the impacts of pollution, timbering, agriculture, and damming of rivers, research on the diversity and conservation status of freshwater mussels is very urgently needed to propose specific conservation measures for these species in Vietnam. If all taxa listed as Data Deficient are found to be threatened, with around 42% of species threatened, this fauna would be one of the most threatened freshwater molluscan faunas in Asia.

During 2007 and 2008, we surveyed freshwater mussels with timed searches at 35 sites in the Niangua River basin, an Osage River tributary in west-central Missouri. Our objective was to determine the distribution, species richness, and abundance of freshwater mussels in the basin. We observed a total of 714 live individuals from 20 species, including the Missouri endemic and species of conservation concern Lampsilis brittsi. The mean catch per unit effort (live mussels/person-hour) was 12 with values ranging from 0 to 144. Eurynia dilatata was the most abundant species (387 individuals observed, relative abundance = 54.2%), but all other species were present at much lower numbers. Eurynia dilatata and Venustaconcha ellipsiformis were the most commonly encountered species, both occurring at 24 sites. Our observation of 20 species is lower than historical richness in the basin (32 species), and nearly all species were formerly more widely distributed in the basin based on the occurrence of weathered and subfossil shells. Together with low catch per unit effort at most sites, these data suggest a sharp decline in mussel populations throughout the basin over the last few decades. This decline is cause for concern, but the causes are unknown.