Identification of Dermocystidium anguillae Spangenberg, 1975 from the American eel Anguilla rostrata (Lesueur, 1817) and Chinese perch Siniperca chuatsi (Basilewsky, 1855)

Recently, mass mortality of the American eel Anguilla rostrata (Lesueur, 1817) and Chinese perch Siniperca chuatsi (Basilewsky, 1855) caused by dermocystidiosis has occurred in China. In the present study, a Dermocystidium species from American eels and Chinese perch was identified. Sequence analysis revealed that the small subunit ribosomal DNA (SSU rDNA) of Dermocystidium specimens infecting American eels was identical to those of Dermocystidium specimens infecting Chinese perch, which indicates the conspecificity of these Dermocystidium specimens from different hosts. When the present Dermocystidium specimens infecting gills of American eels was compared with all reported Dermocystidium species, it is found that the present species has closely related host fish, identical infection site, and overlapped size with D. anguillae Spangenberg, 1975 described from gills of European eel A. anguilla (Linnaeus, 1758), which suggests these two Dermocystidium isolations from the American eels and European eels may be considered as same species. Surprisingly, BLAST search showed that all the newly obtained SSU rDNA of D. anguillae were most similar to that of D. fennicum Pekkarinen, Lom, Murphy, Ragan, Dyková, 2003 infecting common perch Perca fluviatilis Linnaeus, 1758. However, their sequence variation should be within the degree of intraspecific sequence variation, being 99.61% to 99.71% similarities, suggesting that D. fennicum is synonymous with D. anguillae. Phylogenetically, all species in the Dermocystidium genus were clustered in the Dermocystidium clade. However, Amphibiocystidium ranae Pascolini, Daszak, Cunningham, Fagotti, Tei, Vagnetti, Bucci et Rosa, 2003 infecting frog Rana esculenta Linnaeus, 1785. was also placed in this clade, which may either imply the non-monophyly of the species in the Dermocystidium or the requirement for further phylogenetic study on these two genera.