The Goldfish Parasite Chilodonella

The Goldfish Parasite Chilodonella


Chilodonella is a prevalent ciliated protozoan parasite and a common killer of goldfish. Under a microscope the chilodonella parasite appears leaf or heart shaped with a granular inside and a pharyngeal basket that appears as a clear bubble on the front side of the organism. These characteristics disappear after the organism dies; 5-7 minutes after a body scrape is taken. The dead organisms can be confused for what goldfish ich looks like under a microscope.

Chilodonella parasites can lie dormant for long periods but an outbreak can occur when a goldfish has a weak immune system caused by injury or stress. Goldfish stress is typically brought on by presence of poor water quality and improper goldfish care. A goldfish that has not been properly quarantined prior to being placed into a goldfish tank or pond can also easily infect a goldfish community.

Chilodonella Symptoms

Eventually a sick goldfish with Chilodonella parasites will show some or all of the the following symptoms.

  • Clamped fins
  • Isolation
  • Excessive slime production
  • web-like hemorrhages on skin
  • Gasping at the surface (late stages)

Chilodonella Treatment

The most effective chilodonella treatment is aquarium salt. Aquarium salt can sometimes be harmful to aquatic plants not always making it the preferred treatment for chillodonella. Formalin
and potassium permanganate are alternative options.

Formalin: Use 2 milliliters per 10 gallons (38 liters) for two hours then do a major water change. Repeat this daily to treat the ciliated protozoan. Word of caution: dispose of formalin if it contains a white precipitate. This is extremely toxic to fish. Increase aeration during treatments, bypass filter media and avoid using it in water temperatures above 80*F (27*C)

curious goldfish

Potassium permanganate: Add 2 level teaspoons to 1gallon of distilled water and mix thoroughly. Use 3 tablespoons (45ml) of this mixture per 10 gallons. When the tank water turns from purple to amber, add hydrogen peroxide to deactivate the potassium permanganate. Follow the instructions on the bottle of potassium permanganate carefully to avoid doing more harm than good.

Reviewed By: Tim Winter

Tim Winter has a strong affection for pets and wildlife. His years of experience caring for various types of pets has led him to share his knowledge with others on the best practices in pet care. Tim holds a Bachelor of Science from the University of Oregon School of Journalism and Communications.

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1 thought on “The Goldfish Parasite Chilodonella”

  1. I bought from the aquarium shop the parasites chemical, the lady told me to get a big pail add anti chlorine/ salt and the parasite medicine. I put all the gold fish in the pail of water with air pump, end all of them died this morning.

    Any suggestion please let me know.



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