<i>Microsporidium</i> sp. in the Trunk Muscle of Coho Salmon <i>Oncorhynchus kisutch</i> Raised in Sea Cages in Japan

Sea-caged coho salmon Oncorhynchus kisutch in Tottori Prefecture, Japan, afflicted by microsporidiosis, exhibited clinical symptoms that include cyst formation and partial myoliquefaction of the trunk muscle. Analysis of small subunit ribosomal RNA gene sequences revealed that the isolated microsporidium showed high similarity to Microsporidium spp. of marine fishes, including M. seriolae, the causative agent of beko disease in Seriola fishes. Phylogenetic analysis placed the isolated microsporidium in the same clade as M. seriolae, indicating that the microsporidium infecting O. kisutch is an undescribed species closely related to M. seriolae. This is the first report of beko disease in salmonids.