To allow fish to float and not sink to the bottom, many fish have one or two air-filled sacs known as a swim bladder. These bladders expand and contract as needed to move the fish up and down in the water. A fish with swim bladder disease (SBD) will have obvious difficulty getting up off the bottom of the tank and may swim at odd angles.
Several causes of swim bladder disease have been identified, while others researchers are still investigating. Viruses, parasites and bacterial infections can affect the lining of the bladder. Fish that have been bred to create unusual shapes, such as fancy goldfish, have a prevalence of this condition. The bodies of these fish pinch and put pressure on the swim bladder so that it does not function as it should. The dried fish pellets and other dry foods that are a staple for many aquarium fish can also lead to swim bladder problems. These dried foods, when eaten quickly, will soak up fluids in the belly of the fish. This causes an unnatural expansion of the stomach that puts pressure on the swim bladder.
Upon first noticing the condition in any fish in a tank, a partial water change is the first step to combat swim bladder disease. Improving the water quality will improve the health of the fish. If the cause is a parasite, bacterial or viral, owners can help the fish's immune system fight off the disease by giving them the healthiest environment possible. In addition, KokosGoldfish.com reports that "recent research has closely linked high nitrate levels with SBD." After the initial water change, owners need to follow up with more frequent partial water changes until the condition of the fish has improved. For example, if the tank water is typically changed every two weeks, increase this to twice a week.
Peas fed to the fish will help move food through the fish, relieving the pressure on the swim bladder. Another option is to not feed the fish anything for two to three days. This will have the same effect but take more time. To prevent the condition from reoccurring, switching to a more natural diet will help prevent bloat-caused swim bladder disorders. This can be done by feeding peas and zucchini and soaking fish food prior to feeding.
Every fish species has a particular set of environmental conditions it needs in order to thrive. In particular for swim bladder conditions, temperature is very important. Fish kept at too low of a temperature for their species needs will have a digestive system that works too slowly, backs up and puts pressure on the swim bladder. Adjusting the water temperature, in this case usually increasing it, to what is appropriate for the fish species will help resolve many cases of swim bladder problems.
Medication to treat swim bladder disease is a last resort after all other treatments have failed. Several medications are available, but choosing which one to use is done by trial and error since the exact cause is usually unknown. Fish speciality stores can guide owners on using medicated fish food, antibiotic or anti-parasitic medication.