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.

• Abnormal or irregular swimming patterns
• Complete loss of physical balance
• Swimming upside down
• Sinking to the bottom of the aquarium or having trouble surfacing

There are several treatments for swim bladder disease:

• If illness is present, due to infection, and can be diagnosed, treating the illness should also cure the swim bladder disorder.
• Consult with an aquatics specialist for guidance in treating with antibiotics or salt.
• Change tank water frequently, as often as once per day.
• Test your water to ensure there aren't any imbalances. Also, check your heater and air pump to make sure they are working correctly.
• During treatment, perform frequent water changes.

• Water quality: Make sure the water is clean and in top condition to prevent the growth of bacteria and viruses.
• Keep aggressive fish separated to prevent fighting.
• Use caution when handling, netting and transporting your fish.