Neon Tetra Disease in Fish

A Parasitic Ailment That Affects Many Fish Species

Neon tetra fish

 Oscar Sánchez Photography / Getty Images

Named after the fish that it was first identified in, neon tetra disease strikes many members of the tetra family, and other popular families of aquarium fish are not immune. Cichlids such as angelfish and cyprinids such as danios, rasboras, and barbs also fall victim to the disease. Even common goldfish can become infected. Interestingly enough, cardinal tetras are more resistant to the ravages of this disease than the similar-looking neon tetra.

What Is Neon Tetra Disease?

Neon tetra disease refers to a condition caused by a Microsporidian parasite that's more common than many aquarium enthusiasts realize, and affects species beyond neon tetras. The disease is degenerative, meaning it starts mild but then progresses quickly to become very severe.

Symptoms of Neon Tetra Disease in Fish

In neon tetra disease, you're likely to observe symptoms in this order:

  • Restlessness
  • Fish begins to lose coloration, often in one part of the body
  • As cysts in the muscles develop, the body may become lumpy
  • Fish has difficulty swimming
  • In advanced cases, the spine may become curved
  • Secondary infections such as fin rot and bloating

During the initial stages, the only symptom may be restlessness, particularly at night. Often the first thing an owner will notice is that the affected fish no longer school with the others—a clear sign that something is wrong. Eventually, swimming becomes more erratic, and it becomes quite obvious that the fish is not well.

As the disease progresses, affected muscle tissue begins to turn white, generally starting within the color band and areas along the spine. As additional muscle tissue is affected, the pale coloration expands. Damage to the muscles can cause curvature or deformation of the spine, which may cause the fish to have difficulty in swimming. It is not unusual for the body of the fish to have a lumpy appearance as the cysts deform the muscles.

Rotting of the fins, especially the caudal fin, is not uncommon. However, this is due to secondary infection rather than a direct result of the disease itself. Bloating is another sign of a secondary infection.

Causes of Neon Tetra Disease

Neon tetra disease is caused by a parasite called Pleistophora hyphessobryconis. Spores enter the fish through ingesting the bodies of infected dead fish or from eating infected live foods, which may serve as intermediate hosts.

Once inside a fish, the parasite will eat the fish from the inside out, starting with the digestive tract and stomach. Sporoplasms develop inside the intestines, burrow through the intestinal wall into the skeletal muscles, and there they produce cysts. The cysts damage the tissue; signs of tissue damage include paler color and weaker muscles.

It's important to know neon tetra disease is highly communicable and can easily spread through a tank quickly. To save your fish, you will need to remove infected fish as early as possible.

One of the slightly comforting aspects of this disease is that it is at least not transmittable to humans.


There is no known cure for neon tetra disease; in fact, most fish found to have the disease are euthanized. To ensure all fish are not lost, remove diseased fish from the tank so they are not eaten by other fish when they die. Some species, such as angelfish, may live for quite some time with the disease, but they should not be allowed to do so in a community tank. They should be quickly separated from uninfected fish to avoid spreading the disease.

How to Prevent Neon Tetra Disease

The best prevention is to avoid purchasing sick fish and to maintain high water quality. Also, it's important to remove sick fish from your community tank as soon as possible: there is no real cure for the disease, and more so, many fish will eat other dead fish when given the chance.

When purchasing fish for your tank, select a well-regarded supplier. If buying online, be sure to check out any reviews and avoid buying for price versus quality. If possible, though, buy locally. This will give you a chance to carefully observe the suppliers fish. Do not purchase any fish from tanks where there are sick, dying, or dead fish present; you can usually identify a sick fish because it will not school with the others (assuming that the fish you're selecting are schooling fish).

Once you've selected your new pets, quarantine new fish for two weeks before adding them to an existing community tank. This will give your fish a chance to adjust to a new environment while also allowing you to observe their behavior and appearance. If you see any signs of sickness, get in touch with your supplier and avoid allowing questionable fish to interact with others.

Maintain high water quality and select fish foods from a known and respected source. As with any fish or fish supplies, it's easy to wind up with contaminants even if you purchase high-quality fish food. The risk is greater, though, if you buy online at the lowest cost.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
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