White bubbles that develop on a fish's body are most likely caused by "ich," a protozoan-caused disease whose full name is Ichthyophthirius multifiliis. The protozoans dig into fish's scales and fins, creating tiny white spots or bubbles on the fish's surface. Other possible causes of white bubbles on a fish include fish pox and a more serious ailment called gas bubble disease.
Ich or White Spot Disease
Ich or white spot disease frequently occurs when new fish are introduced into an aquarium with existing fish. Fish, plants, rocks and aquarium water imported from an infected tank can harbor the protozoans that cause ich. These creatures swim through water, seeking hosts. When they find a host, they burrow into the scales and fins to feed and reproduce. The white spots you see are the cysts where the protozoans burrowed. The cysts burst forth with a cycle of little protozoans. Ich medicine for fish is readily available at pet stores.
Fish pox, like chicken pox, is caused by a virus. Fish pox occurs mostly on fish who like cooler water, such as koi and goldfish. White, gray or pink spots appear on specimens who acquire fish pox. While the disease looks ugly, it doesn't harm the fish; most recover on their own in seven to 10 days. The disease can recur, however, and new fish introduced into the water may develop fish pox even though symptoms have cleared from your existing fish. Increasing the water temperature can prevent fresh outbreaks of fish pox.
Gas Bubble Disease
You may be contributing to a serious disease that forms clear bubbles on affected fish's bodies when you do water changes. Fish are sensitive to sudden, dramatic changes in water pressure or temperature, and many municipalities aerate the water supply -- if you use tap water from such a supply, the aerated water can change the pressure enough that it forces gas bubbles out of the fish's bodies, out onto their sides. Rapid water temperature changes can cause gas bubbles to form on a fish's scales, too. A white fish may seem to have white bubbles on his sides, but gas bubble disease usually are clear.
Good Hygiene Prevents Problems
You can prevent all three possible causes of white spots or bubbles on a fish with good aquarium hygiene. When choosing fish from a pet store, choose only healthy fish from aquariums where all of the fish seem healthy. If one fish in the aquarium has white spots or is sick, chances are good all of the fish are infected. Never change all or most of the water in an aquarium abruptly using water straight from the tap. Use aquarium water treatment kits, found at pet stores, and let water stand for several hours so it reaches room temperature or close to the same temperature as the aquarium water.
Jeanne Grunert has been a writer since 1990. Covering business, marketing, gardening and health topics, her work has appeared in the "Chicken Soup for the Soul" books, "Horse Illustrated" and many national publications. Grunert earned her Master of Arts in writing from Queens College and a Master of Science in direct and interactive marketing from New York University.