Costia



One of the four most common parasites found on koi in South Africa is Costia, which has killed numerous of our precious Living Jewels.

Also known as Ichthyobodo, it is an external parasite that is quite difficult to identify, even with a microscope. You need at least a 200 x magnification to properly identify it, and one of these cheap R 300.00 microscopes is not recommended to identify Costia. It is one of the smallest parasites common to Koi hobbyists and is often overlooked on a slide.

When viewed under the microscope, it looks very similar to the tiny moving air bubbles in the water, except that the air bubbles will move into one direction, and Costia will move backwards and forwards, almost like bumping cars at a play park, trying to dig through the mucus on the slide.

Physical symptoms on the fish will be excess mucus production, lethargy, clamping of fins and scraping.

You will probably notice reddening of the skin and especially the fins. If you see that your koi hangs at the air stones or water returns, it is an indication of the presence of Costia.

Fortunately it can be eradicated quickly with a high concentration of salt(5kg/1000 liters), but if you don't treat early enough, you might loose fish, especially the small one, as Costia develops rapidly on small fish. A salt bath at 1 kg / 50 liters will also do the trick.

Other recommended treatments are Malachite Green, Potassium, or even Methylene blue, and a once off treatment are normally sufficient, due to the very short life span of Costia. I personally use FMC (Malachite green and formalin) if I do not have a high concentration of salt in the pond, alternatively only salt at a high concentration (5kg/1000 l) , being a much safer and more natural treatment without any possible side effects of other medication.