Most fish, freshwater and saltwater, have a swim bladder, which is filled with gas and helps fish maintain their vertical position in the water. However, in freshwater fish, infection or physical injury to the swim bladder may cause fish to have swimming problems and total loss of physical balance.
There are many different types of swim bladders and fish may have two ways to fill the swim bladder with air. Some fish have a direct connection with specialized blood vessels enabling gases to cross into and out of the bladder according to the fish's needs. An inflated bladder creates buoyancy; a deflated one creates less buoyancy. Some fish have a direct connection between the esophagus and the swim bladder that enables them to control buoyancy by gulping air to fill it. Some scientists believe the swim bladder also produces sounds for some fish through vibration.Symptoms
There are several treatments for swim bladder disease: