Pleistophora hyphessobryconis is the organism commonly known as neon tetra disease and named after the first fish in which it was identified.
More common than some aquarists think, it can affect more species than just neons. Although it usually strikes members of the tetra family, it has also been found in barbs, rasboras, angelfish, and even goldfish. Interestingly enough though, cardinal tetras, Cheirodon axelrodi, are resistant to the disease.
Known for its rapid and high mortality rate, a cure is so far unknown. Immediate removal of the diseased fish is required as the disease starts its cycle when parasitic spores enter the fishes after they eat infected material, like the bodies of the dead fish, or through live foods such as tubifex worms, which may serve as intermediate hosts.
Once in the intestinal tract, the newly hatched embryos burrow through the intestinal wall and produce cysts within the muscle tissue. Muscles bearing the cysts begin to die and the necrotic tissue becomes pale, eventually turning white.
Symptoms of neon tetra disease are;
restlessness
colour loss
difficulty swimming
body becomes lumpy as cysts form
spine may curve in advanced cases
secondary infections like bloat and fin rot
Initially, the only symptom may be restlessness, especially at night. The affected fish doesn’t school with the others and its swimming becomes erratic and it is obvious the fish is sick.
As the disease progresses the affected muscles start to turn white, usually within the colour band and areas along the spine. This pale colouration gets bigger as additional muscles are affected. Damage to the muscles can cause deformation of the spine making it difficult for the fish to swim. Sometimes, as the cysts develop and deform the muscles, the fish’s body will look lumpy.
Rotting fins, especially the caudal fin, is common but this is due to secondary infections rather than the neon tetra disease itself, as is bloating.
Many reported cases of cures are a result of misdiagnosis as certain bacterial infections mimic this disease. Some protozoan drugs are said to alleviate symptoms but this hasn’t been substantiated with scientific studies.
Not all neons are carriers but if the disease is present in one specimen in a tank, it may have already infected all the other neons in the tank. Never buy fish from a tank with sick or dead fish. Fish that do not school, or hang apart from the others, must be suspect.
To prevent disease, quarantine all new fish for at least two weeks and maintain high water quality.
Once infected, it is nearly impossible to rid a tank of the parasite if there are infected fish present. Anytime one fish picks at another, they are at risk of contracting the disease. Although spores may be present in many aquariums, careful cleaning and maintenance will remove most of them. It is only when a fish consumes the spores that they become infected.
Ref: http://freshaquarium.about.com/