A goldfish that floats upside down at the bottom of the tank may have swim bladder disease, as stated by FishChannel.com. This is a syndrome with many potential causes, including infection, shock, injury or deformity.
Swim bladder disease occurs when the fish is unable to swim normally in the tank. The fish may sink to the bottom of the tank, float with its head pointed downwards or even float upside down.
There or multiple causes of swim bladder syndrome. In goldfish, particularly fancy varieties, the problem is commonly a result of swim bladder deformity. The fish may swim normally most of the time, but when stressed or injured the syndrome presents itself. They are more prone to developing swim bladder disease from constipation or an injury to the bladder.
Goldfish owners can prevent this problem by keeping their goldfish healthy and providing a fiber-rich diet, as stated by FishChannel.com. If the syndrome does occur, move the fish to a separate hospital tank with slightly warmer water, about 9 degrees hotter than the other tank. Keep the fish here until it heals and is able to swim properly. If the problem is constipation, feed a chopped up green pea to the fish. This fibrous legume can ease problems within a few hours. If the syndrome persists, owners may need to have a specialist perform surgery on the goldfish swim bladder.