Bob Gray was good enough to dig this up from his archives and post it to the Goldfish Mailing List. This is the best summary I've seen of causes for and treatments of goldfish floatation problems. There are many other treatments, both mainstream and "fringe", but this should be enough to get anyone started. I will add a few comments at the end.


By Doug Thamm

"Why does my goldfish tend to float at the surface of the water and have a hard time going to the bottom of the tank?"

Because it's got swim bladder disease.


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.


  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.


(Note: Some of this stuff is pretty far out, but effective.)

  4. Partial pneumocystectomy. This is another word for surgical removal of part of the swim bladder. I mention this less as a practical option but more just to let people know that there are vets out there doing X-rays, surgery, general anesthesia, even cancer chemotherapy on fish. If you're interested in more information on this procedure, E-mail me and I'll give you more details and a journal citation if you want.

But the best thing to do is to prevent it from happening in the first place.

I'll just add a few of my opinions to Doug's excellent article. Diet seems to be far and away the most common cause of abnormal floating behavior. Look at the poops: they should come out in quarter or half inch chunks. Long, stringy poops are indicative of diet problems (though all fish have one of these every once in a while). To treat, I would start with: (1) fasting for a few days, and then (2) limited feedings of green peas popped out of their skins. I have read recommendations of cleaned earthworms as also being a laxative food, but I have no experience with this. I would view using a syringe to remove air from the swim bladder as a reasonable, but last ditch, way to buy time while treating a fish with really severe floatation problems, provided you are sure the problem is actually the swimbladder! Have a vet do this.