Black Spot:
Black Spot, or diplopstomiasis, often follows the addition of new aquarium fish. All fish are susceptible, especially the Silver Dollar and Piranha. It is fairly easy to diagnose and treat.

External Bacterial Infection:
Bacterial infections are often difficult to diagnose due to the many different types. Orange or red streaks on the body is usually the only fool-proof method for the determination of a bacterial infection.

Cataracts:
Cataracts are fungal growths on the eyes. Treatment with any aquarium fungicide should work. Its probability increases with water rich in ammonia or nitrates.

Corneybacteriosis:
Corneybacteria causes swelling in the head which will push the eyes outward. It is caused by overcrowding and water of poor quality, having an excess of ammonia and / or nitrites.

Dropsy:
Dropsy is not a disease. It is, however, very often a symptom of the internal bacterial infection, that has been classified separately.

Fungal Infections:
This is a very common disorder which infects all kinds of tropical fish. It is intensified greatly with fish having damaged fins or cuts and scrapes. It is also much more likely in poor water conditions in which there are unacceptable levels of ammonia or nitrites. Fungal infections are also a sign of bullying by other fish. Fin nippers will damage the fins of other fish making them more susceptible to fungal infections and external bacterial infections such as fin and tail rot.