This disease effects the gills rather than the entire body. This is also treatable by medications that are sold at pet stores, most commonly used are the antibiotics such as maracyin and tetracycline. This will appear in your fish as a white fuzz similar to a wool or cotton like appearance. If this is left untreated it can spread rapidly across the fish, killing it and other tank members. When purchasing a fish medication make sure that it treats fungus.
Fish can also get bacterial infections.
This is brought on by fighting among the fish in the tank, biting and nipping. The fins appear ragged and split and may be streaked with blood. Other bacterial infections also brought on by fighting include skin ulcers. Also, prompt treatment of this with fish medication can take care of the problem. Fish are also subject to viral infections which tend to be on the serious side.