Isolation and identification of Dermocystidium sinipercae sp. n.

To accurately identify the pathogen of Siniperca chuatsi, the experiments were based on morphological comparisons, combined with parasitic characterization and molecular phylogenetic methods to carry out the study and observe the ultrastructure. The results showed: fusiform or dumb-bell white sporangia, about 1.9-6.8 mm in length, were observed in the fins, skin, oral cavity, gills, the outer and the inner layer of the operculum of the diseased fishes; endospores of (9.8±1.8) (7.3-13.8) μm in diameter; the ring-like cytoplasm and circular refractive bodies of about (6.5±1.2) (3.9-8.3) μm in diameter. It was identified as Dermocystidium. The measured values of this species were different from those of other Dermocystidium and were in general agreement with those of the undetermined species (HB) parasitizing the gills of Siniperca chuatsi; it was parasitized by similar sites as Dermocystidium from Guangdong and Henan provinces (GD and HN) and Dermocystidium sp. (HB). Molecular sequence alignment and phylogenetic results showed that this species shared over 99% similarity with Dermocystidium sp. (HB and HN), Dermocystidium anguillae , D. fennicum, and D. salmonis in SSU rDNA sequences. Phylogenetic analysis indicated that D. anguillae sampled from Guangdong (GD) and Henan province (HN) branched closely with the present species, then D. salmonis, D. anguillae, and D. fennicum. We concluded that Dermocystidium sp. infecting Siniperca sp. are conspecific and we revised the records of the D. anguillae (GD and HN) isolates of Siniperca chuatsi; we named Dermocystidium in this study together with the isolates (HB, GD and HN) as Dermocystidium sinipercae sp. n.. The intraspecific morphological variation of Dermocystidium sinipercae sp. n. may be related to the sampling time and developmental environment; spore proliferation and differentiation processes were recorded and described in ultrastructural observations. This study confirms that Dermocystidium sinipercae sp. n. has been distributed in many parts of China, emphasizing the urgent need to implement quarantine measures for the origin of Siniperca chuatsi.