Sat. Jun 8th, 2024

Costia Parasite

Costia is a single cell microscopic parasite that attacks the skin of fish. It is a flagellate. It destroys the skin, in mild cases the skin appears cloudy, in severe cases the skin is open and bleeding. It usually attacks fish in a poor state of health or living in poor water conditions or in overcrowded conditions. Secondary bacterial and/or fungal infections can occur at the open sore area. Costia can only survive on fish. If it is without fish for 1 hour or more it dies. It can not live in temperatures greater than 86 degrees F.

Treatment recommendations are as follows:

  1. High heat, 92 degrees F. for four days (recommended treatment by Dieter Untergasser, 1989)
  2. Salt bath can be used at 3%, or 7.5 tablespoons/gallon until fish “rolls over,” then put fish in clean water (by Dr. Neville Carrington, Maintaining a Healthy Aquarium, 1985, Salamander Books) or (salt bath of 2.5 tablespoons/gallon for 10 to 15 minutes)
  3. Salt in aquarium at 2 tablespoons/10 gallons to help prevent secondary bacterial/fungus infections
  4. Methylene Blue may be added to aid in preventing secondary infection
  5. Formalin may be used if the skin does not have open areas
  6. Copper based antiparasitics (if used can be difficult to remove from the water if the need arises to switch medications, cannot be used at the same time as many other medications)
  7. Lowering the pH to between 5.0 and 6.0 can aid in prohibiting the parasite, and aid in preventing secondary infection. Lower pH also helps the fish to build slime coat.


  • Handbook of Fish Diseases by Dieter Untergasser, TFH Publications, Inc 1989
  • Maintaining a Healthy Aquarium by Dr. Neville Carrington, Salamander Books 1985
    In this article signs and symptoms include labored breathing, flashing and rubbing, lethargy and lying on the bottom with clamped fins. Treatment can be with PP, chloramines –T, salt, or malachite + formalin.
    The parasite reproduces by dividing in two. Heavy breathing, rubbing, lethargy and skin cloudiness are signs and symptoms of Costia. Treatments can be salt baths, malachite + formalin, or PP.
    Treatment here is acriflavine or copper sulfate. The skin can come off with this disease leaving bloody patches.e above general symptoms, the best way to identify it is to take a scrapping of the affected area and look at under a microscope and look at it as a wet mount. This bacteria is actually piles up and forms columns that move under the scope – hence the name. This bacteria is a major problem in aquaculture and has been studied pretty extensively. A real good general article is put out by the Southern Regional Aquaculture Center, Pub #479. Download it at