Occasionally, captive fish may appear to have small clear or white bubbles on the outermost layer of the skin. Depending on their appearance and dispersion, these bubbles may indicate an injury or infection.
If a fish scratches its skin against rough substrate or coarse ornaments, the skin wounds may gather small air bubbles.
Ich is a fairly common disease affecting both saltwater fish and freshwater fish. This contagious parasite causes small, white spots on a fish's skin. Ich spots may resemble bubbles, but they are solid masses.
Aquarists can differentiate air bubbles from ich spots by observing whether or not the spots break apart under moving water. Air bubbles caused by skin abrasions should break away from the fish's skin when the fish is near a filter; however, spots caused by ich will remain.
Minor abrasions on a fish's skin usually resolve without treatment; however, a stress coat formula can help to speed a fish's recovery. If the bubbles are caused by ich or another infection, prompt treatment can prevent the infection from becoming life-threatening.
To prevent skin abrasions and parasitic infections, maintain a low-nitrate, high-oxygen water supply and quarantine all new fish before adding them to a tank. Remove all rough ornaments and substrate if your fish seem prone to skin injuries.