Morphological and Molecular Approaches to Differentiating Dermocystidium spp. 

Jonah A. Nguyen1, Justin M. Stilwell2, Ethan T. Woodyard2, Celene M. Slifka1, Divya Rose2, Matt J. Griffin2, Thomas G. Rosser1

1Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, 240 Wise Center Dr, Mississippi State, MS 39762; 2Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, 240 Wise Center Dr, Mississippi State, MS 39762.

ABSTRACT

Dermocystidium is a cosmopolitan parasite of fish and is at the phylogenetic boundaries of both animals and fungi. Some species are associated with mortality in aquaculture and wild fish, making identification to species important. Identification is currently done using morphological features, host species, and sequencing of small subunit ribosomal DNA (18S). The morphological basis of species identification is complicated by few distinct features and limited variation among known species. The use of molecular data to differentiate Dermocystidium spp. also presents challenges, as the 18S rDNA region is highly conserved among Dermocystidium spp. This obfuscates whether host species is a reliable indicator of Dermocystidium species. To help bring clarity to differentiating members of this genus, redspot darters Etheostoma artesiae were collected in Oktibbeha County, Mississippi, US over multiple sampling events between April 10 and May 8, 2022. Some harbored large ovoid cysts of a Dermocystidium sp. beneath the skin. Ruptured cysts revealed spherical spores containing a prominent refractile body. Morphological features of the spores were measured and compared to other Dermocystidium spp. in the literature. The 18S rDNA was sequenced and was found to be 99.76-99.94% similar to Dermocystidium sinipercae, a parasite of Chinese perch Siniperca chuatsi from China. To obtain and assess additional molecular markers and bring more clarity to the identity and taxonomy of the Dermocystidium sp. from this study, next generation sequencing was performed. Based on that data, primers were designed to amplify partial large subunit ribosomal DNA (28S), partial cytochrome C oxidase (cox1) and partial cytochrome B (cytb). The morphological and molecular data herein along with histopathological observations will bring clarity to identifying Dermocystidium to species.