Molecular Identification, Phylogenetic Analysis, Clinical and Histopathological Findings of <i>Dermocystidium anguillae</i> From Koi Carp ( <scp> <i>Cyprinus carpio</i> </scp> )

Dermocystidium is a pathogenic fungus-like protist that infects many fish species, causing lesions on the skin, gills and other tissues, which may result in systemic disease. In the present study, a new Dermocystidium anguillae infection in the skin and eyes of the koi carp (Cyprinus carpio) from Iran was described using a comprehensive analysis of morphological, histological and molecular data. Filiform hyphal-like cysts were visible on wet mounts. The cysts were filled with spherical to round spores. Wet mount preparations of fresh cyst contents of Dermocystidium anguillae revealed a massive number of spherical to oval spores with refractile bodies. The spores were approximately 5-13 μm in diameter. In histopathological examination, the skin and eye masses were infiltrated by numerous elongated cystic structures. The eosinophilic and hyalinised wall of the cysts was 4-6 μm thick and filled with numerous spherical spores with eccentrically situated nuclei and a large refractile body. In the dermal layer, around the cystic structures, there was edema and granulomatous dermatitis (infiltration of moderate numbers of plasma cells, small lymphocytes and epithelioid cells). Oedema, hyperaemia and multifocal haemorrhages were evident in the ocular masses. The nucleotide sequencing results obtained from the GenBank BLASTN database indicated a 100% sequence similarity with the registered Dermocystidium anguillae.