Chilodonella and Costia

10.2.5. Chilodonella and Costia

A patchy greyish-white “beat up” look on the body with some spider-webbing and a roughened appearance is indicative of an infestation by a microscopic external protozoan parasite such as Chilodonella or Costia (Ichthyobodo).

This is oftentimes difficult to differentiate from bullying. The patchiness is typically rather diffuse as opposed to the more well-defined white spots caused by ramming during aggression. And there is typically some excess mucus evident in chilodonella and costia.


Chilodonella and Costia on two fish
Chilodonella and Costia on two fish

In severe cases, these protozoan diseases can cause so-called “slime coat disease” where the mucous on the scales of a fish is literally sloughing off. These fish need a so-called “shotgun approach” with both ich and fluke medications in the water and broad-spectrum antibiotics in the food. This is covered in this link:

11.13. Slime Coat Disease

There are a whole series of protozoan diseases that can present themselves exactly like chilodonella and costia. These diseases include trichodina and tetrahymena. Occasionally epistylis will present just like this. The fact that the diseases are different is only found when microscope smears are taken of the skin. Treatment of all these diseases is similar:

  • Add a formalin/malachite green medication (Ich-X, Rid-Ich Plus, Blue Planet White Spot Remedy and Mardel QuickCure) or a Copper based medication (Cupramine, Copper Power, Copper Aide or Copper Safe) to the water of the aquarium to kill the free swimming organisms.
  • Add lots of additional biofiltration (under-gravel, canister or sump) to filter out and thus kill the free-swimming organisms. This added biofiltration also reduces the bacterial loading in the water which in turn allows the fish to devote more immune system resources to the pathogen.
  • Do not put the fish in a hospital/quarantine tank
  • Do not change out or clean the filter media.
  • Do not raise the temperature of the tank
  • Add a 24/7 UV sterilizer to kill the free swimming organisms and reduce the bacterial loading in the water which in turn allows the fish to devote more immune system resources to the pathogen.
  • Added aeration always is helpful

These treatments will typically work for both chilodonella and costia.

Startpage Aquariumscience

Source: – David Bogert

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