Anchor worm, fin rot, dropsy and skin flukes are all common diseases for fish kept in aquariums. The causes and treatments for these diseases vary, and without quick treatment, the affected fish may die.
White or green threads protruding from a fish's skin along with a scratching by the fish may indicate a diagnosis of anchor worms. These worms burrow into the skin and muscles of a fish before growing to adulthood. Treatment consists of an over-the-counter parasite medication.
Bacterial infections can cause a disease known as fin rot, in which the fins of a fish progressively decay, fray and fade in color. Aquariums that are not cleaned regularly can contribute to the development of these bacteria. Treatment for fin rot consists of properly cleaning the aquarium and, if necessary, applying an over-the-counter antibiotic to treat the fish's bacterial infection.
If the abdomen of a fish swells and the scales start to protrude, this indicates a case of dropsy, caused by a bacterial infection of the kidney. Fish that are healthy may not require treatment, but proper treatment of the water and aquarium conditions is necessary to reduce the dropsy-causing bacteria. Fish that are weak or unhealthy may require antibiotic shots or other treatments to heal.