Morphological re-description and molecular characterization of Chloromyxum thymalli (Myxosporea: Chloromyxidae) infecting the gall bladder of Hovsgol grayling Thymallus nigrescens.

Abstract

Chloromyxum thymalli infects the gall bladder of fishes belonging to the genus Thymallus. Here, we provide morphological, histological, and molecular data to complete the original description. Rounded plasmodia measured from 25 to 30 µm in diameter and contain 8 developing spores at most. Spores are typical of the genus Chloromyxum. Mature spores are subspherical, (mean ± SD) 9.05 ± 0.08 µm (range: 7.75-10.03 µm) long, and 8.81 ± 0.09 µm (range: 7.19-10.01 µm) wide. Four pyriform polar capsules are equal in size, 3.4 µm long and 2.7 µm wide on average. Histopathological analysis showed that presporogonic stages were found in the lamina propria under the epithelial cells of the host's gall bladder and destroyed the integrity of the epithelium. The obtained SSU rDNA sequences of C. thymalli did not match any available sequences in GenBank. Phylogenetic analysis showed that C. thymalli forms a sister cluster with C. truttae, with a subclade of Chloromyxum spp. that infect the gall bladder of freshwater teleosts.