Chilodonella (ciliates) are unicellular ectoparasites, i.e. parasites that live on the surface of their host’s body. 

Chilodonella can be easily identified under the microscope by its oval, flat shape and gyrating swimming movements. Chilodonella is about 40 to 70 micrometres long and has a notched body end.

If Chilodonella (ciliates) occur in small numbers, they do not pose a great threat to a Koi. However, the parasite can become a problem, especially in overcrowded, heavily polluted ponds. Here the parasite first attacks already weakened Koi, and then also spreads to the healthy animals. Whether a Chilodonella infestation is present can only be determined by examination under the microscope can be clearly determined, since a Chilodonella infestation is very similar in its symptoms to other parasitic infections.

The infestation usually begins with Chilodonella (ciliate lashes) in the gills, which in the Koi can lead to shortness of breath

As a result, the koi shows strong gill movements and hangs apathetically on the surface of the pond. Other symptoms include pinched fin, listlessness, loss of appetite and shy, extremely hasty escape reactions. 

If the infestation has progressed, there is also an excessive build-up of mucus on the gill covers and in the head area. This is visible through a white-blue clouding of the skin and can go from the neck to the dorsal fin and the tail. In extreme cases, the skin can peel off like fragments. If the Chilodonella infestation is not recognized in time and treated accordingly, the gills that can pass through parasite infestation are almost completely stuck together. The fish suffocates as a result.

In order to treat a Chilodonella (ciliate) infestation, the water quality must first be improved. 

Even a generous change of water can prove to be extremely helpful here. In the initial stage, measures such as KPM (potassium permanganate), table salt or a 40% peracetic acid usually prove to be effective. 

If secondary symptoms such as bacterial infections occur in the Koi, treatment with antibiotics is necessary, whereby the dosage instructions of the veterinarian or the respective manufacturer should be observed.