Chilodonella Symptoms and Treatment

Chilodonella is one of the hottest fish killers there is.

It’s a ciliated protozoan parasite.

Under the scope you may see a heartshaped organism, or a large round organism full of tiny bubbles.

Alive, the Chilodonella resembles a heart shaped onion, with a fuzzy end where you could imagine the onions roots would be. These are actually cilia.

Dead, Chilodonella are motionless round balls full of tiny bubbles. This makes them hard to recognize. They may resemble Ich but they do not have a crescent nucleus nor do they move at all, in their dead, rounded state.

Chilodonella Symptoms and Treatment
Chilodonella Symptoms and Treatment

Chilodonella reproduces sexually and also by binary fission.

Chilodonella Treatment

Chilodonella clears EASILY with salt. Leave the salt in for 14 days, and be sure to supplement aeration, as gill damage d/t Chilodonella may be severe in the survivors. Chilodonella should be suspected anytime large numbers of fish are dying on the surface, or who roll over on their sides.  Except when disturbed, the Koi seem to be roused from stupor and dash about madly.

Chilodonella Symptoms and Treatment Water Temperature

Chilodonella works in any temperature but ice cold, and super hot water is NOT its favorite. Normally, losses are heaviest, and the organism most active, in the cooler water of Springtime.

Chilodonella seems to be universally sensitive to salt at 0.3 – 0.6% 

Chilodonella is easily recognized under the microscope and can be compared to the organism as shown in our movies section. 

Chilodonella’s “saltwater counterpart” (salt water version) is Uronema.


Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.