2021 Volume 56 Issue 3 Pages 130-139
A microsporidian disease showing abnormal petechiae-like red spots on the trunk muscle, beneath the skin, occurred among rainbow trout Oncorhynchus mykiss farmed in Shiga Prefecture. Numerous microsporidian spores were detected from the affected area and the causative agent was identified as a microsporidian closely related to Kabatana takedai based on morphology and molecular analyses. Anecdotal information indicated the possible involvement of common prawn Palaemon paucidens for the transmission of the pathogen. Three prawn feeding trials using O. mykiss and Biwa trout Oncorhynchus masou subsp. successfully reproduced the disease in both fish species. The microsporidian infections were confirmed in the fish given fresh and chilled prawns and mortalities occurred in these groups. No infection occurred in the groups fed with frozen prawn. These results strongly suggest that the microsporidian infections can be lethal to Oncorhynchus spp. and that P. paucidens plays important role in the transmission of the pathogen. These findings may lead to the elucidation of the multi-host lifecycle of fish microsporidians.
