White bumps on fish are almost always indicative of disease or injury, although on occasion the bumps are perfectly normal. When the cause is disease, fish with white bumps need to be isolated from other fish and immediately treated. Stress is a common factor with white-bump issues in aquarium fish, such as fighting with other fish or scraping against aquarium decorations. Removing the stress factors help greatly in reducing the possibility of disease.
Ich is one of the most common of the white spot diseases that inflict aquarium fish. This protozoan disease is present in virtually all aquariums, but healthy fish usually develop an immunity to it. When a fish is stressed repeatedly, his immune system weakens and that is when ich attacks. Ich causes itchy white bumps on the fish's skin that get worse with time and eventually cover the gills, causing respiratory distress and, finally, death.
White sores are usually caused by scraping the scales off a portion of the fish's skin through overly strenuous activity in the tank, which allows infection to get past the skin's defenses. Fighting with aggressive fish and bumping into sharp aquarium objects can peel off the scales, and that is when white sores develop. These are often large, white areas that are sometimes indented but can also appear as raised white areas or bumps.
In this case, the raised, white spot is a worm sticking out of the skin. The skin itself turns red from bleeding around the area where the worm penetrated. Removing the worm using tweezers is the recommended treatment, but this can be difficult as the anchor has to be removed to prevent infection from setting in. Introducing aquarium salt into the tank helps not only to heal the wound but to kill the worm as well.
Cotton Wool Disease
This bacterial fungus-like condition afflicts not only the body of the fish but also the mouth areas as well, where it becomes known as cotton mouth disease. The disease begins with white spots in the area of infection, which soon grow fluffy white, cotton-like fuzz. In some cases, these spots appear like white bumps until the fuzz grows in fully. Left untreated, this disease eats away the face, head and torso of the fish, causing death.
Breeding Tubercles on Male Goldfish
When male goldfish reach breeding age, they display small, white bumps on their fins and gill covers. These are called tubercles and are perfectly normal. This is how many aquarists tell the difference between mature female goldfish and the mature males. These tiny bumps remain on the fish throughout the spawning season, which is late spring and early summer for most areas, and vanish as quickly as they came when the spawning season is over.