Myxobolus nagaraensis (Myxozoa: Myxosporea) was first reported in 2007 in freshwater gobies (Rhinogobius sp.) from Nagara River in the Gifu Prefecture, Japan. Although freshwater gobies are common fish species found in rivers of the Kanagawa Prefecture, infection of these fishes with M. nagaraensis has not been reported. Therefore, this study surveyed for M. nagaraensis infection in freshwater gobies from Sakai River, which runs through the Kanagawa Prefecture. Freshwater gobies were captured using hand nets at different locations along the Sakai River in November 2017 and February 2018. Diseased fish displaying enlarged abdomens and nodules in the caudal peduncle were caught from 2 locations which were 20 km apart. Cysts excised from these diseased fish contained parasitic spores resembling the morphology of M. nagaraensis. DNA was extracted from the cysts and the small subunit ribosomal RNA gene was amplified (SSU rDNA). Based on homology search, the amplified partial product was 99.6% identical with M. nagaraensis SSU rDNA (Accession no. AB274267). This is the first report of M. nagaraensis infection in freshwater gobies from a river in Kanagawa. Since prevalence of the parasite and its pathogenicity to the goby populations are still unclear, continued examination of other rivers in the prefecture is crucial.
