Chilodonella is one of the fastest fish killers there is. It can cause large numbers of fish to die on the surface of the pond. Often fish infected with Chilodonella will become lethargic and even begin to roll over on their side, only to quickly upright themselves and swim off when disturbed. Under a microscope, they resemble the shape of a man’s ear and move around acting like a bumper car as they run into things.
One of the reasons it can be such an effective killer is that unlike many parasites, they tolerate a wide variety of different temperatures. That means that Chilodonella can still be a threat to koi even at very low temperatures when your fish are least likely to fight them off.
It can be identified through skin scrapes and gill biopsies from its characteristic slow gliding movements, often turning in circles. Chilodonella can be treated in a couple of different ways. Malachite Green and Formalin is the most effective, but potassium permanganate can also be effective. Potassium Permanganate is, unfortunately, much harder on your fish than treating with Malachite Green and Formalin.