Costia (ichthyobodo)

  • Main symptom : the early stage can be difficult to recognize, because the parasites involved are tiny organisms (narrower than a human hair). The fish skin becomes milky, covered with an opaque whitish to grayish veil. Overproduction of mucus and slimy patches (it is sometimes called slime disease). The infection usually starts with a few patches and then develops rapidly on the rest of the body.
  • Secondary symptoms: The fish scrapes itself against aquarium objects and may develop red sores. Labored breathing when gills are infected (fish may hang at the surface of the aquarium). Be careful not to confuse these symptoms with those of ammonia/nitrite poisoning.
  • Direct causes: protozoan flagellate only visible under a microscope (200x or better 400x) invading the skin and/or gills of fish. As the parasite is very small, without a microscope, it can be confused with gyrodactylus.
  • Contributing factors: any stress factor (poor aquarium hygiene, poor transport conditions). Check the water quality: it should have 0 ammonia, 0 nitrite and low nitrate. Also check your pH is your water is soft. As is often the case, fish are often healthy carriers of parasites but the development of parasites is controlled by the fish’s defenses. In case of stress, however, they can start to proliferate, which is serious.
  • Contagious: yes.
  • Occurrence: not very common.
  • Severity: serious.
  • Treatments : AquaCare Anti-Parasite, SERA Costapur, Waterlife Protozin. It is generally advised to temporarily and gradually increase the temperature of the tank by two to three degrees during the treatment in order to accelerate the parasite’s life cycle. Aquarium salt (see below) can also be added.
Fish with costia - close view

Costia is characterized by a milky opaque veil on the skin of the fish, with overproduction of mucus.

Question marksAquarium salt: The addition of aquarium salt in addition to a commercially available treatment. Recommended salt dosage for goldfish: 1 tablespoon per 15-20 liters (4-5 US gallons) speeds up the process of eliminating the parasites that cause costia and adds electrolytes to reduce osmotic stress. Be careful not to overdose the salt in the aquarium: it does not evaporate (after a water change, only add the dose corresponding to the volume of water that has just been changed). Also be careful when using salt if you have other species of fish in the same tank: some species are intolerant to it. Aquarium salt can be found in pet/fish shops, but any 100% natural non-iodised salt is suitable; do not use table salt! When the treatment is finished, partial water changes will allow the salt to be gradually eliminated.
Exclamation markImportant: do not forget to remove any activated charcoal during the entire treatment period (as it will absorb the drugs). Activated charcoal can be put back in the aquarium at the end of the treatment.
Good hygiene and water quality can prevent the re-occurrence of this disease.
Exclamation markImportant: Whilst all care is taken to provide accurate information on this website, Web Goldfish accepts no responsibility in the case of mis diagnosis of diseases/ incorrect treatments or any other errors made. In case of doubt, please always consult a veterinarian.