Freshwater pearl mussels are critically endangered in the UK, surviving only in a handful of clean upland rivers. Their conservation requires exceptional water quality and a complex dependency on specific salmonid fish hosts.
Freshwater pearl mussel welfare science is complicated by uncertainty about mollusc sentience. Current evidence does not establish that mussels experience suffering in the way that vertebrates do. However, their conservation has welfare significance through the ecosystem services they provide: mussel beds filter river water, improve clarity, and create habitat complexity that benefits many vertebrate species with clearer welfare interests. The parasitic larval stage on fish gills raises a question about welfare impact on the salmonid host: fish parasitised by glochidia show local gill tissue response but without evidence of systemic welfare impact when infestations are moderate. The recovery programme for freshwater pearl mussels is one of the most complex in UK conservation, requiring simultaneous restoration of water quality, sediment management, salmonid host populations, and reintroduction of captive-reared juveniles.