Ich Treament Guide | White Spot Disease on Fish


What is Ich?

Ich is a disease that affects many freshwater fish, and it is caused by protozoan parasite Ichthyophthirius multifiliis. Ich is also known as “Ick” or “White Spot Disease.”

Parasites are routine problems for aquarists and could be worms, crustaceans (such as lice), or most often protozoa. Ichthyophthirius multifiliis is a protozoan parasite whose name literally means “the fish louse with many children.” Protozoa are single celled animals that are either free living or parasitic. Under the lens of a microscope Ich has sphere shape with a rolling motion, propelled by its cilia. Adult organisms, unlike the infective stages, have a C shaped nucleus. The saltwater version of Ich is caused by Cryptocaryon irritans.

When contracted, the parasite matures in the fish’s skin where it can hide from treatment in the water. It can penetrate the gill epithelia, fins, and epidermis. Once developed, it will leave by rupturing through the skin, leaving the fish more vulnerable to infections and parasites. In large numbers this can even directly kill the individual by destroying the integrity of the fish’s surface. Certain freshwater fish may be more susceptible such as catfish, rainbow trout, and eels. 

Life Cycle of Ich


This parasite has a “direct” life cycle, meaning it does not need any intermediate hosts to complete transmission. Ich is also an “obligate” parasite, meaning it must have a fish host to survive. Their life cycle is very dependent on water temperature and can go from 7 days long at 25 °C to 8 weeks at 6 °C. It has been known to go through a life cycle in as little as 8 hours as well. There are 3 basic life stages for Ich, a parasitic trophont, a reproductive tomont, and an infected theront. We will explore these life stages below

Ich Treament
Ich on fish

1. Tomont 

The mature trophont leaves the infected animal by rupturing through the skin and becomes a tomont. The tomont then sinks towards the bottom, attaches to a surface, and forms a thin-walled cyst. Within this capsule the tomont divides many times into tomites, up to as many as 2,000. This is the reproductive life phase. 

2. Theront

As the infective stage of the parasite, once they mature in the tomite cyst they push their way out of and are released into the water. Now mobile they swim around in the water column looking for a host. The hair like cilia appendages beat in rhythm to propel around. When they find a host, they then burrow into the fish’s epithelium using a penetrating gland and their cilia. This life phase is the most vulnerable to treatment. If the theront is unable to find a host within a couple of days it will perish. 

3. Trophont

After the theront burrows under the skin it becomes a trophont. This protective cyst stage shields it from all known treatments for Ich, using the fish’s own mucous and epithelium as a barrier. As the trophonts mature you will see the classic white spots its known for. Researchers have shown this mature stage  to able to reproduce under the skin directly without going through the full life cycle. When this happens you may seen multiple cells of similar size lined up together. Unfortunately when Ich reproduces in this manner, it is essentially untreatable.

Symptoms of Fish with Ich

  • Small blister like white spots externally on the fish
  • Lethargy, increased respiratory effort, and/or loss of appetite
  • Flashing or scratching themselves on objects in the tank. 
  • Scale loss or bruising secondary to flashing 
  • Balance disturbances
  • Increased respiratory rate or distress

Fractures of the fin cartilage or fin ray fractures are generally not life threatening but can look very similar. Male goldfish can also produce white bumps on their pectoral and/or operculum fins when breeding. An experienced aquarists and amateurs alike will have little trouble identifying the common signs with this almost ubiquitous parasite. Next time you visit a pet store, take a close look at their fish and see if you can spot any signs of Ich in their population, chances are you may.

Treatment for Fish with Ich

Due to its complex life cycles, Ich can be challenging to treat. The trophont encysted stage is generally not affected by treating your tank, as it is protected by the fish’s skin and mucous. Once your tank becomes infected, all life phases will be present. After your first treatment only a percentage of the parasite will be eradicated. Thus, you will likely need to treat multiple times, with an average of three to seven treatments. After three treatments your tank should be reevaluated by a fish health professional to decide if further medication is warranted. The temperature of the water will affect how quickly the parasite’s life cycle progresses. For example, at 75F or higher you likely will treat daily, where as at 45-54F you may treat every 3-4 days. Your aquatic health professional can better guide you on the specifics for your tanks and its population.

Many options to treat Ich are available. Salt, a longtime friend of aquarists, is one of the best preventative and treatment for Ich. It is more effective for recirculation systems, but may be too costly for ponds.

A variety of over the counter treatments may also contain Malachite green, a dye that has controversial use in aquaculture. This chemical is reported to have carcinogenic, mutagenic,  and teratogenic effects. It’s even toxic to your respiratory and can cause chromosomal fractures. Should you choose to use this product, be very careful with it and do not use with any system that has fish meant for ingestion.

A 37% solution of formaldehyde in water with 6-15% methanol preservative can be used as a bath treatment or a pond treatment. Formalin should also be handled cautiously, as it can be dangerous to humans. Copper Sulfate (CuSO4) is one of the most affordable chemical treatments for this parasite and is generally safer to humans. This treatment is determined by the water’s total alkalinity concentration. Another option, Potassium Permanganate (KMnO4), oxidizes organic material in the water including bacteria living on the surface of the fish and protozoan parasites.

A close eye should be kept on your recovering fish, as they can be weakened from the infection. Fish with visible spots may appear ok, until the adults rupture through the fish’s primarily protection. The defects left behind have to heal in before becoming infected with something else. While not the most desirable solution, in cases of chronic resistant infections there is the option of completely starting over.

How to Prevent Ich

Prevention is always preferred to treatment in the case of Ich. One of the easiest and often essential prevention measures it to quarantine any new fish before adding them to your tank. Ideally this should be for at least 30 days. New fish could be asymptomatic carriers that with the stress of leaving the pet store and acclimating to a new environment, may see an outbreak 1-3 weeks later. When picking out a new fish make sure to check out the health of the individuals in surrounding tanks. While there may not be any obvious signs in the tank you’re picking from, they may have shared equipment between systems, or a system that run several tanks off of one large aquarium filter.

The tomont is very sticky and easy be transferred between systems by “fomites” such as nets, siphon hoses, cleaning equipment, etc. It’s best to have separate equipment between tanks and their own individual filtration system to avoid transferring illness between populations. Ich could also be spread in water aerosolization, so keep this in mind when planning where to put your tanks.  Quarantine is essential to large public aquariums with new arrivals being isolated, monitored, and generally treated for parasites before being introduced into their system. Depending on the aquatic species you may also want to adjust their isolation for longer. As always, good water quality, low stress, and good nutrition are important for the health and vitality of your fish.

Ich vs Velvet Disease

Velvet Disease, often known as “Rust” or “Gold Rust Disease,” is another parasitic disease commonly encountered by aquarists. Some scientists consider it a protozoan and others as an algae, since it has chlorophyll. Velvet Disease has a similar life cycle and similar symptoms to Ich. The tomite penetrates the skin, fins, and gills; destroying cells and feeding on the nutrients inside.

This parasite produces finer golden spots instead of white. Many times they are so fine they may missed until the fish perishes. It’s generally present in the majority of commercial aquariums, but often is only a problem when the fish is stressed by poor water quality, temperature changes, or transportation. One trick to attempt to more readily see these fine spots is to direct a beam of a flashlight onto the fish in a dark room. Seen more on the fins and skin, “Rust” can also infest the gills. The disease can affect all fish, even those a few days old, and has both a fresh and salt water versions. The treatment and prevention are similar to Ich, with quarantine again being crucial to prevention.

We hope that this general overview will help you better identify, treat, and prevent Ich in your system. As with most disease in the aquarist hobby, quarantining new animals before introducing them to your established system will identify and isolate the spread of infections.

Fish Laboratory

With decades of collective fishkeeping experience, we are happy to share the fish care tips that we've picked up along the way. Our goal at Fish Laboratory is to keep publishing accurate content to help fishkeepers keep their fish and aquarium healthy.

Recent Posts