Chilodonella viewed at 400x under a miscrope

Chilodonella cyrini is another microscopic protozoan that can be deadly to freshwater fish. The protozoan is an accomplished swimmer, and can quickly infect an entire pond’s stock of koi fish. In ponds with large populations, it can spread quickly and be devastating—especially to younger fish.

The fact that this parasite is most effective in colder water, from 40-50ºF, makes it more dangerous to your koi. At these temperatures, your koi’s immune system is not at full capacity and can succumb more quickly to the parasites.

Chilodonella can be introduced to your pond by a number of vectors. As it can remain dormant, a seemingly healthy, non-symptomatic pond mate can bring it into a healthy pond. Live food and plants will allow the parasite to hitch a ride. Even unwashed hands and nets can move it from one pond to another.

Chilodonella can also be a secondary pathogen, piggybacking through damage done by other parasites (like Costia), or open wounds and sores.

Identification of Chilodonella

Single chilodonella in a microscopeUnder a microscope, Chilodonella is described as ear- or heart-shaped with small hairlike structures (called cilia) on the larger (ventral) side that are used for swimming and feeding.

Chilodonella might not have a catchy nickname, but due to its size, identifying it can be tricky. It will require a skin scrape or gill biopsy of a live fish, as the parasite leaves the host (your koi in this case) when it dies.

Additionally, Chilodonella is a little shier than costia (meaning it is slower moving), so even at 100x magnification it can be more difficult to spot than some other faster-moving parasites.

It can reproduce through two different means—more commonly through binary fission (where it simply divides) but also conjugation.

Symptoms of Chilodonella

As is typical of the koi’s responses to invasive parasites, there are a number of symptoms of chilodonella—many of which are similar to other parasitic infestations that affect the gills. They include:

  • fins clamped
  • flashing
  • rubbing
  • gasping at the surface
  • floating on their sides until disturbed
  • more time near airstones or waterfalls (increased oxygen areas)
  • increased mucous production
  • skin looks cloudy
  • appetite loss
  • weight loss

It is mainly the shoulder region between the head and dorsal fin where the parasite’s effects are most noticeable. Portions of the body will take on a milky appearance as the chilodonella eat the skin. When there is visible swelling, and skin starts to peel off in strips, the infection is at an advanced stage.

Treatment for Your Koi

Even though this is one of the more deadly parasites, it only becomes dangerous in environments where a koi is stressed enough to give it a foothold. Maintaining good water quality, cleaning scratches or wounds, and not overstocking your pond are all preventative measures to stop outbreaks from happening.

If you diagnose your pond with Chilodonella, there are treatments that effectively combat its spread and damage to your koi population.

  • Malachite Green and Formalin
  • Potassium permanganate
  • Salt dip (2.5%)
  • Salt bath (0.5%)

Caution: Manufacturers’ dosage recommendations may vary. Make sure you follow their instructions. Also, be wary of how weakened your koi is. The treatment may be too much for it to handle.

Potassium Permanganate can be harsh on your koi, and especially on those koi already weakened by the parasite. The full dosage and treatment duration might have to be modified to accommodate these koi.

Extra aeration will help a koi that is already struggling to breathe. Feed your koi in smaller doses, as they will be less likely to eat large amounts. This also will lessen the waste product load that uneaten food will cause.

Don’t raise the temperature, as it will have no effect on this parasite.

At Next Day Koi, we appreciate the stress treating koi illnesses. It’s why all of our koi fish for sale undergo a rigorous 14-day quarantine protocol before they are marked for sale.

If you are looking to stock your pond at some of the best shipping rates in the industry, contact us and we’ll be happy to get your next living jewel to you.

1 response

  1. Don Krech :

    For how long of a time can Chil stay dormant, how long can they survive without a host. Can they be killed during dormancy. Thanks

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