Myxozoa, or myxidium serotinum-myxobolus koi.
This parasite infects many types of genera and species.
If you suspect an infection, check the gall bladder for cysts and spleen with crushed saline mounts of gill tissue size around 0.2-1.
The infection is past via faeces. Your fish are not the main host, the latter is not known.
It is quite rare, most infections occur in small koi under 6". It can be a problem with gills, although this infection is treatable, in most cases it does little harm.

Read More Articles On Fish Health CLICK HERE