Microasite, viz. Plistophora hyphessobryconissporidian par. Typically infects "Neons" and other closely related characins, but has now spread to several other species. Also infects salmonids.
Very contagious, usually fatal. No treatment except complete sterilization.
Microsporidiosis in Zebrafish Research Facilities
From Content public journal Volume 53 No. 2 2012
Justin L.Sanders et al.
Dr. Jacobs, Bruno
Fish Medical sprl