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.
Proliferative kidney disease (PKD) is a widespread temperature-dependent disease in salmonids caused by the myxozoan parasite, Tetracapsuloides bryosalmonae (Canning, Curry, Feist, Longshaw et Okamura, 1999) (Tb). Tb has a two-host life cycle, involving fish as an intermediate host and freshwater bryozoans as the definitive host. Although salmonids are acknowledged as hosts for the parasite, it is less clear which fish species are active hosts in the life cycle of Tb. Differences in infection dynamics have been observed between some fish species, which are thought to be related to the existence of two main Tb-strains, the American and European. Iceland, having three species of indigenous salmonids and positioned geographically between Europe and North America, is an ideal location to study the natural development of Tb in wild fish. The main aim of this study was to determine the genetic origin of Tb in Iceland and confirm whether mature spores are produced in Icelandic salmonids. In this study, Icelandic salmonids were infected with the European Tb-strain. In situ hybridisation revealed that intraluminal sporogonic stages, including mature spores, were commonly observed in all three salmonid species. The presence of intraluminal stages has previously been confirmed in brown trout Salmo trutta Linnaeus and Atlantic salmon S. salar Linnaeus in Europe, but they have only been observed in Arctic charr Salvelinus alpinus (Linnaeus) in North America, infected by the local strain. This is, therefore, the first time that sporogonic stages have been observed in Arctic charr in Europe, where fish are infected with the European Tb-strain. Our data strongly suggest that all the three salmonid species inhabiting Icelandic waters serve as active hosts in the life cycle of Tb. However, for full confirmation, transmission trials are needed.