Neon Tetra Disease in Fish

Causes, Treatment, and Prevention

Neon tetra fish

 Oscar Sánchez Photography / Getty Images

Neon tetra disease is a degenerative condition caused by parasites that is both fast-spreading and fatal to fish. Named after the species that it was first identified in, this 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, cardinal tetras are more resistant to the ravages of this disease than the similar-looking neon tetra. This condition is typically caused by a fish eating infected live food or consuming the remains of infected dead fish in the tank. Once affected, fish begin to lose their coloration, develop cysts, and have difficulty swimming before the disease progresses to a severe infection, ultimately leading to death. There is no known cure for neon tetra disease, so prevention is essential.

What Is Neon Tetra Disease?

Neon tetra disease is a condition caused by a microsporidian parasite that's more common than many aquarium enthusiasts realize, and it affects species beyond neon tetras. The disease is degenerative, meaning it starts mild but progresses quickly to become very severe. The parasite consumes the fish once infected, affecting its muscle tissue and often leading to secondary infections.

Symptoms of Neon Tetra Disease in Fish

The symptoms of neon tetra disease typically develop in a certain pattern as the parasite progresses. When a fish becomes infected, tank owners will likely 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.

Loss of Coloration

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.


Cysts often begin to form in the muscles of the fish as the parasite infects these areas. It is not unusual for the body to have a lumpy appearance.

Difficulty Swimming

Damage to the muscles can cause curvature or deformation of the spine, which may cause the fish to have difficulty in swimming. Because the muscles are primarily affected, even those without curved spines can experience impaired movement.

Secondary Infections

Bloating in the body or rotting of the fins (especially the caudal fin) is not uncommon. However, these conditions are both due to secondary infection rather than direct results of the disease itself.

Causes of Neon Tetra Disease

Neon tetra disease is caused by a parasite called Pleistophora hyphessobryconis. Spores enter the fish by being consumed as food, typically through these two methods:

  • Fish ingests the bodies of infected dead fish
  • Fish ingests live food that is contaminated with this parasite

Once one fish is infected, the disease can also spread to others through damaged skin or gills or via transovarial transmission from parents to offspring. After the spores enter 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. While the disease was first identified in the neon tetra species and named for these fish, it has also been observed in many others including cichlids like angelfish, cardinal tetras, goldfish, and cyprinids such as danios, rasboras, and barbs (and additional common species can also be infected).

Is Neon Tetra Disease Contagious to Other Animals?

It's important to know that neon tetra disease is highly communicable, and the spores can survive in water for months. If healthy tank habitants ingest the body of an infected fish, it can easily spread through a tank quickly. One of the slightly comforting aspects of this disease is that it is not transmittable to humans.

Diagnosing Neon Tetra Disease in Fish

Spores of Pleistophora hyphessobryconis can be visually seen in the tissue of infected fish, and diagnosis may involve examining this tissue. Symptoms of this parasite can be compared to similar diseases to determine the cause, though microsporidian diseases in fish are considered untreatable. Fish may be quarantined when signs are first noticed to observe their progression and rule out other conditions.

Treatment and Prevention

There is no known cure for neon tetra disease. To ensure all fish are not lost, any affected fish should be quickly separated and removed from the tank. Many fish will eat other dead fish when given the chance, so this is a necessary step to prevent the disease from spreading to healthy fish.

The best prevention methods are to avoid purchasing sick fish and to maintain high water quality. When purchasing fish for your tank, select a well-regarded supplier. If buying online, observe any reviews and avoid buying for price versus quality. When possible, buy locally. This will give you a chance to carefully inspect the supplier's 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 prevent questionable fish from interacting 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. However, the risk is greater when buying online at the lowest cost.

Prognosis for Fish With Neon Tetra Disease

Since microsporidia are not treatable, fish infected with Pleistophora hyphessobryconis parasites will eventually succumb to the condition. Some species, such as angelfish, may live for quite some time with neon tetra disease, but they should not be allowed to do so in a community tank. Most fish found to have this disease are euthanized before it becomes debilitating.

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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