Disease of free freshwater and ornamental fish due to an infection with the holotrich ciliate Ichthyophthirius multifiliis , which lives between the epidermis and the corium. Infection can be diagnosed by the occurrence of white dots on the skin (= other name for the disease: white-dots disease). Fish try to get rid of the apparently itching parasites by scrubbing at stones etc.; their fins are kept compressed. If gills are highly infected, fish show apathy, do not feed, are seen in a lateral upside-down position, do not show escape-reflexes and may die due to inflammation of the skin lesions within 4–5 days.