Diagnose and Treat Saltwater Ich (Cryptocaryon)

Learn to Diagnose and Treat White Spot Disease

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Saltwater Ich or White Spot Disease is caused by an infestation of the ciliated protozoan Cryptocaryon irritans. Although other parasites such as Oodinium (Velvet or Coral Fish Disease) and Brooklynella (Clownfish Disease) can also cause spots on the fish at one stage in their life cycle, Cryptocaryon progresses more slowly. If detected early and treated promptly upon an outbreak, the chances of recovery are high. However, in a closed aquarium system, it can reach overwhelming and disastrous numbers if it is not treated appropriately.

The Life Cycle of Cryptocaryon irritans

  • Free-swimming cells, called tomites or theronts, are released from a mature tomont, or cyst, and go in search of a host fish, typically dying in a day or two if one is not found.
  • Upon finding a host the tomites attach to the gills or body and develop into the feeding stage, called trophonts, which burrow into the fish and begin feeding on its tissues. The epithelium of the fish swells over the trophont, which makes the visible white spot.
  • Once well fed,usually after 3 to 7 days, the trophonts stop feeding and encyst in order to reproduce. These dormant cysts, called tomonts, can remain trapped in the fish's mucus, be embedded deep in the tissue, or drop off and fall to the bottom. Over a period of 6 to 12 days (varies by water temperature) the cells inside the tomont cysts reproduce by cell division to become 100 to 1000 new tomites. Once reaching maturity the cysts rupture, releasing hundreds of new free-swimming tomites, and the cycle begins again.


Unlike Oodinium and Brooklynella that typically attack the gills first, which allows these diseases to advance into life-threatening levels quickly as they go unnoticed, Cryptocaryon usually appears at the onset as salt-sized white spots visible on the body and fins of a host fish, although it can also infest the gills. Because Cryptocaryon is more easily recognized in its beginning stage, it is much easier to treat and cure before it gets out of control.

Aside from the appearance of the white spots, fish will scratch against objects in an attempt to dislodge the parasites, and rapid respiration develops as trophonts, mucus, and inflamed tissue clog the gills. Fish become listless, refuse to eat, loss of color occurs in patches or blotches as the trophonts destroy the pigment cells, and secondary bacterial infections may invade the lesions caused by the trophonts.

Treatment Recommendations

Although copper is very effective on Oodinium, and it works well to eliminate Cryptocaryon organisms in their free-swimming tomite stage, it is not effective on the Cryptocaryon trophonts that burrow deeply into the tissues of fish, so the aquarium needs to be treated repeatedly until all of the trophonts mature. Because of the prolonged life cycle of Cryptocaryon, affected aquariums should be treated for a minimum of 3–6 weeks. If the fish are removed from the saltwater aquarium into a quarantine tank, any Cryptocaryon parasites remaining in the aquarium without fish will die after a period of time, up to 4 weeks, depending on temperature.


Copper is toxic to marine invertebrates, so if they are present in the aquarium, the fish should be moved to a quarantine tank for treatment.

A combination of freshwater and formalin treatments administered by means of dips (short duration exposure) or baths (prolonged treatment) over a period of time in a QT is recommended as a treatment in place of copper.

Preventing Re-Infestation

Reinfection will occur no matter how effectively the fish have been treated if Cryptocaryon is not eradicated from the main aquarium, which can be accomplished by keeping the tank devoid of any fish for at least 4 weeks. For fish-only aquariums, hyposalinity can be applied, and to speed up the life cycle of the organisms, elevate the tank water temperature. For marine aquariums that also have invertebrates, or reef aquariums, Ruby Reef Kick-Ich and Chem-Marin Stop Parasites are "reef safe" treatments that specifically target the Cryptocaryon organisms.

Several days prior to returning fish to the main aquarium, clean all filtering equipment, change any filtering materials, and perform a water change.

Medication Usage Tips:

  • Porous materials such as sand, gravel, rocks, and ornaments can absorb medications. To better control the strength and effectiveness of any product you are using, it is best to use a bare QT with only some cut pieces of PVC tubing in the tank to provide shelter for the fish during the treatment period.
  • Although many over-the-counter remedies contain the general name Ich or Ick, carefully read the product information to be sure it is designed to specifically target and treat "Cryptocaryon."