Diseases Diseases

How To Recognize Costia Parasites in Fish


Costia is a known parasite that effects your fish's immune system and can cause lasting problems within the fish's body. Costia can cause ulcers, bacterial infections and rotting fins. Costia is usually found within Koi fish or Goldfish but sometimes can also be found in other species of fish. Costia is very hard to find, as it's so tiny, even under a microscope.

Step 1

Recognizing Costia is difficult within itself. Usually, if a fish is infected with costia, it will show some warning signs. The most common warning sign is an itchy fish. A fish that acts spastic, jumping around and spiraling, may be trying to scratch themselves. Costia parasites are tiny and pesky little creatures, so they will 'tickle' the fish as they go around the tank.

Step 2

In order to actually diagnose your fish with Costia, the fish will need to have a mucus scraping done. This is the only sure way to see if your fish has a costia problem. You may want to take your fish to an aquatic vet, where he or she will use a microscope and investigate. Typically, if anything is moving on the fish's body, it's usually of parasite form and could very well be costia.

Step 3

Treating costia is pretty simple to do. If your fish has costia, it can be cured by using ProForm C or QuickCure. These are products sold at your local pet shop or fish store. Along with these products, you'll need to regularly change the water within the fish tank as a clean fish tank is the proper approach to make sure the costia does not come back. Also, make sure to have lots of de-chlorinator on hand.

Step 4

After treatment, it's very important to pay close attention to your fish. As you should begin to see them being less on edge and begin to notice less 'itching'. You should keep an eye out for growing ulcers on the fish and try to pay attention to you fish's overall behavior.

Step 5

Preventing costia is very important. If you have a case of costia in your fish, it's best to always protect the other fish by quarantining the sick fish until treatment has began. If you're also thinking about introducing new fish to the pond or tank, it's better to keep them away from the infected fish or at least treat them before going in with the new fish. This will help prevent further infestation and will keep your fish healthy.


Contrary to popular belief, the costia parasite cannot be killed by salt. Many people believe that salt can kill this parasite, but the truth is, the costia parasite is immune to this and is salt resistant.


Costia is not something to take lightly. Costia infestations can cause severe health issues within fish and sometimes, it can result in death. These parasites will feed on the fish, particularly the gill and skin cells. Costia will then deprive your fish of necessary oxygen and have the habit of causing other serious infections within your fish, like fungus and bacteria issues.

By Nicole Marie, published at 02/28/2012
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