Neon tetra disease

What is neon tetra disease?

Neon tetra disease is caused by a parasite (Pleistophora) that infects muscle tissue. It was first described in neon tetras but can affect other characins — cardinals, glowlight tetras, black neons, and some other small tetras. Once a fish is infected, there is no cure. The focus is on limiting spread and supporting the rest of the group.

Symptoms

Early signs can be subtle: a fish that lags behind the school, loses colour, or develops pale or whitish patches (especially along the blue stripe in neons). As it progresses, the body may curve, the fish may struggle to swim, and it may lose weight. Not every pale or curved fish has neon tetra disease — stress, poor water quality, or other illnesses can look similar. But if you see these signs in tetras, it’s worth considering.

Does it affect other tetra species?

Yes. Cardinal tetras, glowlight tetras, black neon tetras, and other characins can be infected. The parasite is passed when healthy fish eat infected tissue (e.g. from a dead fish or during aggressive feeding). It does not affect non-characins like danios, rasboras, or livebearers in the same way, though good hygiene still matters.

What to do

• Remove affected fish — Isolate or euthanise humanely. They won’t recover and can spread the parasite if others eat them.
• Don’t add new tetras immediately — Wait and observe. If more fish show signs, the parasite may already be in the tank.
• Support the rest — Keep water quality good, avoid stress, and feed well. Healthy fish resist better.
• Quarantine new tetras — Before adding new characins, quarantine them for a few weeks. See how to quarantine. Won’t guarantee no disease, but reduces risk.

Prevention

Buy from reputable sources. Avoid tanks where fish look thin, pale, or lethargic. Quarantine new tetras before mixing with existing stock. Once the parasite is in a tank, it can persist; some keepers avoid adding more susceptible species to that tank.

Quick takeaways

• Neon tetra disease is caused by a parasite; no cure.
• Affects neon, cardinal, glowlight, black neon, and other characins.
• Remove sick fish; support the rest; quarantine new additions.