Fish Disease Spotlight: Chilodonella

Chilodonella is a type of parasite/protozoa which thrive in water that is fresh. It is shaped similar to a leaf, and has a length which ranges from forty to seventy microns, with a width of between thirty and fifty microns. Its ventral side will usually be cilia covered.

Signs and Symptoms

Chilodonella is similar to other parasites like Costia in that it may remain dormant for extended time periods. When pond fish are under significant stress, or become physically weakened, or the water quality is rarely tested, then this parasite can reproduce rapidly, attacking the gills of the fish.

As a consequence the breathing of the fish may become labored. They will spend more time near the surface trying to get air. They will also become lethargic, attempt to scratch themselves by rubbing their body against various surfaces and will appear distressed overall. You may also notice that their fins fold, or become clamped, and their bodies may begin producing abnormal amounts of mucous, which is the result of the parasite consuming the fish’s epithelial layers.


Once the gills of a fish become afflicted the mortality rate is high. As with other disease, time is a critical factor. The sooner you detect and begin treatment, the lower the casualties. Junior fish are more vulnerable to Chilodonella than adults, since they are still growing and lack the ability to effectively resist.

How To Treat And Prevent Chilodonella

Once the parasite is identified treatment is fairly straightforward. Pond owners can use Formaldehyde or Acriflavine, as well as methylene blue. Whichever one you choose, it is essential to follow the directions of the manufacturer, as different products will require distinct concentrations. As such it is not possible to provide a treatment for Chilodonella which is standardized. Since ponds containing fish usually have other plants and animals present, it is also important to ensure the products you use will not harm vegetation or invertebrates.

Furthermore, when you begin treating the fish, remember to maintain allowances for infection degree. A fish which has become weakened may not be able to withstand a complete dosage, so it is important to adjust either the strength and or length of time in which the medication is administered. Unlike other fish diseases, it should also be noted that Chilodonella is not influenced much by water temperature.

Many pond, aquarium and fish experts consider Chilodonella to be one of the most lethal skin parasites a fish can be exposed to. To prevent it, you must first ensure your fish population is under control, as crowding increases the infection risk. Second, Chilodonella can swim and attach themselves to a variety of objects, which is why pond equipment should be sterilized regularly and anyone handling them should wash their hands. Third, optimal water quality must be maintained at all times, as the ability of this parasite to thrive in clean water is low.