What is the common name for the disease caused by the protozoan parasite Ichthyophthirius multifiliis?

The common name for the disease caused by the protozoan parasite Ichthyophthirius multifiliis is "Ich." This term is widely recognized in the aquaculture and aquarium communities as a shorthand for "ichthyophthiriasis," which is the disease itself. Ich is characterized by the presence of cysts that appear as small white spots on the skin and gills of infected fish, hence the alternative name "white spot disease."

Ichthyophthirius multifiliis infects fish by penetrating their skin and gills, leading to a range of symptoms including lethargy, respiratory distress, and in severe cases, death. Effective treatment often involves increasing water temperature and using specific medications that target the parasitic life stages.

While "white spot disease" accurately describes the appearance of the infection, "Ich" is the more commonly used term among fish keepers and veterinarians when discussing the condition, making it a more precise answer to the question posed.