Fish: White Spot Disease (Ich)

What is white spot disease or “ich”?

White spot disease, also called “ich” (pronounced “ick”), is an infection of freshwater fish caused by a single-celled, protozoan parasite called Ichthyophthirius multifiliis. Affected fish have small, white cysts on their skin, gills, and fins. It is highly contagious between fish.

How do fish get infected with ich?

Fish are usually exposed to the parasite through infected water or the addition of other fish to their environment. The infective stage of the parasite (theront) swims to the fish host and penetrates the fish’s skin. Once in the skin, the parasite (now called a trophont) burrows into superficial layers of skin and gills to feed. When mature, the parasite leaves the fish and is now called a tomont. The tomont attaches to a surface (such as the bottom of a pond) and forms a gelatinous cyst around itself.

Once the cyst is formed, the parasite divides, producing new, infective parasites (theronts). The speed of replication depends on the temperature of the water: they replicate faster in warmer water. Theronts leave the cyst and swim around to find a fish to infect.

What are the signs of ich?

The typical signs of ich are small, white spots on the body or fins of the fish, but these spots usually occur long after infection. Earlier signs of infection include:

• Increased mucus production, which may make the fish look slimy
• Lethargy and decreased appetite
• Flashing (a form of itching where a fish darts to something to rub or scrape against)
• Rapid breathing or gasping at the surface if the parasite has infected the gills

How is ich diagnosed?

A veterinarian knowledgeable in aquatic medicine will assess your fish and discuss the signs. Diagnosis requires a skin scraping or a small biopsy to identify the parasite under a microscope.

How is ich treated?

Treatment of ich is not straightforward, since the parasite is only susceptible when it is moving freely in water, and not when it is in a cyst or in the fish’s skin. Your veterinarian will recommend treating the water with chemicals (formalin, copper sulfate) multiple times.

Your veterinarian will give you specific instructions on how to treat the water, including how often to treat. These treatments should be continued until there is no sign of illness in the fish. Your veterinarian may also recommend re-testing the fish before you discontinue the treatments.

Monitor your fish closely during treatments and follow your veterinarian’s advice for discontinuing a treatment, as some fish may not be healthy enough to tolerate the recommended dose.

Some aquarists worry about treating their fish with chemicals, but there are some natural ways to treat ich, too.

• Raise the temperature: Most strains of ich cannot survive in water temperatures above 86ºF, so slowly raising the temperature of the tank is enough to get rid of the parasite. Not all fish can stand the heat, though. Even for fish that can handle warm water, adding oxygen to the water is essential for this treatment method.
• Add salt: Adding salt can end a new ich infection before it gets too severe. Even freshwater fish can stand a bit of extra salt in the aquarium for a short time, although this method is only suitable for scaled fish. Only use aquarium salt – avoid table salt. Add about a tablespoon of salt per 5 gallons of water, but give your fish time to acclimate. After the infection disappears, change the water multiple times to make sure the salt is totally removed.
• Move all fish to a hospital tank: While this method alone cannot treat an ich infection, it can make it easier to get rid of the parasite and clean the original tank. It also protects plants, substrate, and decorations in the original tank. Keep your fish in the hospital tank for at least 48 hours to make sure the parasites in the original tank die off.
• Move the fish and clean the tank repeatedly: An effective way to clear ich from a fish population is to transfer all the fish carrying trophonts in their skin, fins, or gills to a non-infected tank every 24 hours. In the clean tank, the fish do not get re-infected and, after a few days (dependent on temperature), all trophonts have left their skin and the infection is cleared. Under colder water conditions, these management procedures should be continued over a longer time.
• Mechanically filter: Another control method involves mechanical filtration of water using mesh sizes of 80 microns, which removes the tomonts from the water before they settle and transform to the tomocyst stage.

Keep in mind that treating ich naturally is less effective than using chemical treatments because resistant strains of ich can develop. Using environmental changes along with ich medication is the most reliable way to get rid of ich in your tank.

Use caution when introducing new fish or re-homing the previously infected fish as they can remain carriers.

Can ich be prevented?

Ich is very contagious, so you should quarantine infected fish for at least 30 days before introducing any new fish to their tank. Also, do not share any potentially contaminated equipment, plants, or other tank contents without thoroughly disinfecting them.

What is the prognosis for a fish infected with ich?

The prognosis for fish with ich depends on the number of parasites, underlying fish health, and how quickly the infection is diagnosed and treated. Large infestations can be fatal, especially if the fish is already immunocompromised.