How Protozoa and Parasites Affect Koi Health and How to Treat Them

We will start by covering some of the more common types of protozoan disorders.

In Chilodonella the entire body of the fish is covered with a heavy slime coat. Treatment for Chilodonella requires the use of Metronidazole or quinine sulfate..

When Koi health is affected by Eimeria your fish appear emaciated and have sunken eyes. To treat them you must make a medicated food with either tetracycline or oxytetracycline and feed this to them once a day for 10 days.

Another common protozoal disorder is Ichtyobodo (Costia). Koi that are affected with this disorder have small areas on their bodies that have a blue-gray tinge that looks like excess mucous. Treat these fish with a fungicide/protozoacide dip/bath treatment in the water or quinine sulfate.

When ICH (Ichphyophthirius) strikes your Koi will appear to be covered in white sand or grit and some fish breathe heavily. These fish need to be treated with quinine sulfate or copper sulfate

When Koi health is affected by Heteropolaria (Episapylis), the fish can be seen flashing (Flashing is a fish behavior characterized by rapid, glancing contact with a solid object in an effort to displace an external parasite or other irritation, so called because the light colored underbelly of the fish is thus exposed to momentary view.) and rubbing on objects in the pond, even in the spring when they don’t have any visible signs of the disease. Then in the summer they develop ulcers and bacterial infections.

Usually, if you have treated your pond for parasites and your Koi are still flashing, then Heteropolaria is the cause. Treat this Koi health issue with quinine sulfate and then treat the secondary bacterial infections.

Hexamita, also known as Hole-In-The-Head Disease, is indicated when your Koi exhibit erosions on their heads and gill plates. In severe cases the disease follows the lateral line. The preferred treatment for this disease is the use of quinine sulfate.

Finally, in Trichodina, symptoms include heavy breathing, the fish have a heavy slime coat and appear to have round, flat parasites on them. This protozoal disease should be treated with a fungicide/protozoacide dip/bath treatment in the water.

Next we’ll discuss how parasitic disorders affect Koi health.

When the problem is Gill Flukes, also known as Dactylogyrus, the Koi will gasp for air at the top of the pond. They also sometimes flash, rub against objects in the pond and their gills may develop bleeding. To cure this disorder you need to treat your pond water with an anti-parasitic powder. Treat secondary problems, if there are any after the flukes are gone, with an antibiotic product.

In the case of Anchor Worms, or Lernaea, your Koi will exhibit small pimples on the skin or reddened areas with a white threadlike worm sticking out. To treat Anchor Worms you need to treat your pond water with an anti-parasitic powder.

When Koi health is affected by Fish Lice (Argulus) the fish will have small, round clear to white objects stuck all over them. Your Koi will flash and scratch against objects. Again you should be treating your pond water with an anti-parasitic powder.

If your Koi are infested with Leeches you will see flat and thin brown objects stuck all over the body of your fish. As before treat your pond water with an anti-parasitic powder.

A Tapeworm infestation will cause your Koi to have swollen bellies even if they have not been fed in a couple days. While there is no suitable treatment for severe bloating you can treat for Tapeworm with an antiparasite powder.

In summary you need to be vigilant about keeping a close eye on your Koi and also be aware of what types of treatments are appropriate for different conditions. This article is not meant to replace the advice of a licensed veterinarian. It is intended for informational purposes only. If you are ever unsure about the cause and/or proper treatment of your fish, make sure to contact your veterinarian so that you can ensure optimal Koi health.