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Chilodinella is one of the fastest fish killers there is. It attaches to the skin and gills of koi and severe infections can result in rapid fish losses. Chilodinella is a ciliated protozoan that cannot be seen with the naked eye, and can only be identified with a microscope. It means that a skin scrape must be taken. Chilodinella will appear as a heart shaped organism with rows of tiny hair-like (cilia) extensions along its longer side. It may also appear as a round organism full of tiny bubbles.Staining the slide with Methylene Blue may help if you have never seen this parasite before.


The parasites spread through division. It can swim and infection can easily spread quickly from fish to fish. Infections can occur at all temperatures, with an optimum temperature range between 5 and 10 degrees Celsius. Chilodinella therefore have a head start on Koi during spring when the Koi's immune system is not fully functioning yet.There are unconfirmed reports that Chilodinella can form cysts (Encysting protozoan), and lie dormant untill conditions become favourable again. Koi infected with Chilodinella may display a number of symptoms. These symptoms will differ depending on wheter the Chilodinella infection is limited to the body or also affects the gills. As the parasites are fast moving, it should always be assumed that the gills will also be infected.Large numbers of Childinella are frequently found on on a weak koi suffering from other ailments. It should be noted that if this parasite gets a foothold, some of the koi may not make it throuhg any or all of the treatment, as some koi will be severely weakened.

Symptoms associated with Chilodinella
  1. Koi appearing lifeless.
  2. Hang in the water with fins clamped.
  3. Spend lots of time at air stone or water returns.
  4. Rapid gill movement.
  5. Skin ulcers and bacterial infections may appear.
  6. Stressed appearance with blood vessels showing on the body and fins.
  7. Large numbers are dying.
  8. Fish roll over on their sides and will scuttle away when disturbed.
  9. During initial stages there will be increased production of mucus, causing a white or bluish sheen on the body.
  10. In advanced stages, mucus covering will disappear and the fish will have a “sandpaper” feeling to the skin. The gill may also be damaged beyond repair. If the fish displays a “sunken eye” appearance, it pretty mush had it.

Prevention of Chilodinella
  1. It may attach to nets, live food, hands and containers.
  2. Sterilise equipment and wash hands.
  3. Observe sensible stocking levels or rapid infections will occur.
  4. Good water quality will help
  5. When fish are stressed, the parasite will multiply quickly
  6. Disease is more common during spring and autumn, so temperature fluctuations should be avoided.

Treatment of Chilodinella
  1. Malachite Green and Formalin
  2. Potassium Permanganate
  • My personal choice of treatment is Malachite Green and Formalin.

Updated 11 March 2011

Last Updated on Friday, 11 March 2011 09:15