In the present study, a high percentage of Japanese anglerfish, Lophius litulon (Jordan, 1902), contained a microsporidian infection of the nervous tissues. Xenomas were removed and prepared for standard wax histology and transmission electron microscopy (TEM). DNA extractions were performed on parasite spores and used in PCR and sequencing reactions. Fresh spores measured 3.4 × 1.8 µm and were uniform in size with no dimorphism observed. TEM confirmed that only a single developmental cycle and a single spore form were present. Small subunit (SSU) rDNA sequences were >99.5% similar to those of Spraguea lophii (Doflein, 1898) and Glugea americanus (Takvorian et Cali, 1986) from the European and American Lophius spp. respectively. The microsporidian from the nervous tissue of L. litulon undoubtedly belongs in the genus Spraguea Sprague et Vávra, 1976 and the authors suggest a revision to the generic description of Spraguea to include monomorphic forms and the transfer of Glugea americanus to Spraguea americana comb. n. Since no major differences in ultrastructure or SSU rDNA sequence data exist between Spraguea americana and the microsporidian from the Japanese anglerfish, they evidently belong to the same species. This report of Spraguea americana is the first report of a Spraguea species from L. litulon and indeed from the Pacific water mass.
A new microsporidium was observed in the flying fish Cypselurus pinnatibarbatus japonicus (Franz) (Exocoetidae) from Yakushima, Japan. Visual examination revealed the microsporidium to form white elongate nodules in the host's trunk muscle. Monomorphic spores were ovoid to pyriform in shape, with average dimensions of 4.1 × 2.2 µm and possessing a polar tube describing 13-15 coils. Histological observations showed that each parasite focus of infection was encapsulated by a host-produced fibrous membrane. The presence of sporophorous vesicles was not clearly determined. Ribosomal DNA sequence analyses showed the microsporidium to be discrete from other known fish muscle-infecting species and to be most closely related to a clade comprising the Pleistophoridae and Glugea spp. The parasite is provisionally placed as Microsporidium cypselurus sp. n.