Piscinoodinium sp., a parasitic dinoflagellate infection in the imported ornamental freshwater betta fish (Betta splendens) in Korea

다국어 초록 (Multilingual Abstract)

This study reported the first clinical case of Piscinoodinium sp. infection in the imported ornamental freshwater betta fish (Betta splendens) in Korea. Piscinoodinum is a well-known parasitic dinoflagellate responsible for the disease commonly known as velvet disease, characterized by the appearance of fish caused by the attachment of trophonts. Our specimen originated from a school of cultured betta fish imported from Indonesia. Affected fish exhibited lethargy, dyspnea, and rusty-faded body color. Fresh skin scrapings and sediments contained many trophonts and mature cysts. Actively swimming dinospores, which had emerged from the cysts, were also found. Histopathological observation of the skin revealed that the attached trophonts induced epidermal erosion, flattened epithelium, and massive cellular infiltration. PCR amplification of partial SSU rDNA (small subunit ribosomal DNA) and phylogenetic analysis showed that our specimen exhibited 97.3-97.6 % homology with those of Piscinoodium sp. deposited in GenBank and formed a robust cluster with all the Piscinoodinium sequences. Since there is currently no detailed morphological and molecular description of Piscinoodonium at the species level in the literature, we tentatively identified our specimen as Piscinoodinium sp. Further studies are necessary to clearly identify Piscinoodinium found in this study.