Hope this helps:
Swim bladder disease is a multifactorial illness which primarily affects ornamental goldfish which have globoid body shapes, like orandas, ryukins, and fantails. It most often presents as a fish which floats at the surface, or a fish which stays on the bottom and doesn't seem to be able to easily rise. A fish which has normal buoyancy but is listing to one side or the other often does not have swim bladder disease, but may have other diseases.
In order to understand swim bladder disease, a cursory discussion of fish anatomy and physiology is necessary. The swim bladder is a small epithelium-lined sac in the anterior abdomen which is responsible for maintaining buoyancy. It has a close association with blood vessels such that gases can diffuse across into and out of the sac according to the needs of the fish. The
sac inflates if the fish needs to be more buoyant, and it deflates if the fish needs to be less buoyant. Goldfish and some other fish have a special addition to this system called the pneumocystic duct, which is a connection between the swim bladder and the esophagus, allowing additional adjustment of buoyancy by letting air out through the digestive tract.
People have debated for years over the cause of swim bladder disease. It is pretty well established now that a number of things can cause swim bladder disease. Some of the things which have been suggested are:
1. A virus. The virus attacks the epithelium of the sac and inflammation occurs which makes the epithelium too thick for gases to diffuse across. Thus the fish is stuck at a certain buoyancy because gases have nowhere to go. This may be
more of a factor in non-goldfish species.
2. A Bacterium. There is little evidence to support this, but it's widely known that bacterial infections can cause the same kind of thickening of the swim bladder epithelium as viruses.
3. Anatomy. Globoid-shaped fish like ornamental goldfish are predisposed to problems with the swim bladder because their guts are all squashed up in their abdomen. This arrangement predisposes to food impactions, which in turn clog up the pneumocystic duct.
4. Diet. Feeding dry foods which tend to take on water like a sponge and expand in the fish predispose to food impactions.
See #3 above.
SO WHAT CAN YOU DO TO PREVENT THIS FROM HAPPENING?
1.As always, the golden rule of fish disease is WATER QUALITY. If swim bladder disease does have an infectious cause, your fish will be better able to resist this infection (and others) if your water quality is good. Periodic water changes and
water testing are a must.
2.Pre-soak your flake or pelleted food. This will allow expansion to occur prior to the fish eating it, and will lessen the chance of impaction.
3.Even better, switch to a gel-based food or other food source, i.e. frozen or live food.