If your fish swims upside down it most likely has a swim-bladder disorder/disease. This happens when the swim-bladder, a gas filled organ that controls the fish's buoyancy by inflating or deflating, is unable to control itself and causes the fish to either stay at the bottom of the tank, float helplessly at the top, bob-around head first at the bottom, swim on its side, or swim upside-down. A swim bladder problem can be caused by constipation, bacterial infection, poor water quality, physical damage to the swim bladder, or physical deformity of the swim bladder. This condition is sometimes hard to treat because its often hard to diagnose the cause before its to late.

The first step to take with a fish that has a swim bladder disorder is to test the water quality of your tank. It is usually a good idea to move the affected fish into a 5-10 gallon hospital tank for observation/treatment to ensure that the other fish do not become sick also. A good first act of treatment for an unknown cause of a swim bladder disorder is to try feeding the fish a shelled thawed or cooked unsalted green pea (the green pea is a laxative and will relieve your fishes swim-bladder problem if it is constipated). If this does not help you may want to start the fish on a antibacterial medication. Do frequent water changes at this time because having good water quality will offer relief for the affected fish.

Also lower the tanks levels so that is is about 1/2-2 inches above the fishes dorsal fin (this reduces pressure on the swim bladder causing the fish much relief).If the fish looks swollen that is often either the beginning stages of dropsy or a sign of constipation. If dropsy is suspected than you would want to start the fish on antibacterial medicated food soon! Often fish do not recover from a bacterial infection of the swim bladder. Bacterial infections will usually result in dropsy- which is terminal.