An Outbreak of Neoergasilus japonicus (Copepoda: Ergasilidae) on the Japanese Rice Fish Oryzias latipes Reared in an Outdoor Tank

Abstract

An outbreak of ectoparasitic copepods occurred on the Japanese rice fish Oryzias latipes stocked in an outdoor tank for the extraterritorial conservation program. ​Only the adult female copepods were found on the skin and fins of the host fish. ​The parasite was identified as Neoergasilus japonicus from the morphological characters including an inflated projection on the second segment of the exopod of the first swimming leg, and the single-segmented exopod and endopod of the fourth leg. ​Partial sequence of 28S rDNA and cox1 genes also supported the morphological identification. ​This is a new host record for N. japonicus. ​A bath treatment with 1% salt concentration was effective in detaching the parasite within a day.