Please note: This is intended for people of all different backgrounds and levels of experience. Please don't be put off if some of this information seems too basic, or if some of this information seems unnecessary or superfluous.
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.
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:
- 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.
- 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.
- 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.
- Diet. Feeding dry foods which tend to take on water like a sponge and expand in the fish predispose to food impactions. See # 2 above.
What can I do to prevent swim bladder disease?
- 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. Regular water changes and water testing are a must.
- 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.
- Even better, switch to a gel-based food or other food source, i.e. frozen or live food. You can E-mail me at firstname.lastname@example.org for a recipe for gel food.
Let's say I didn't read this in time. What can I do to treat it?
(Note: Some of this stuff is pretty far out, but effective.)
But the best thing to do is to prevent it from happening in the first place.
- Feed your fish a couple of peas. That's right, peas. Just get some frozen peas, thaw them, and feed them to your fish. A professor of fish medicine at N.C. State College of Veterinary Medicine has done this in several cases with very good results. He thinks that the peas somehow encourage destruction of the impaction. No hard scientific data yet, but it's worth a try.
- Fast your fish for a couple of days. Withhold all food for three or four days, and sometimes this alone will break up the impaction and return things to normal. Most fish can go a week to ten days without food and be just fine.
- Periodic aspiration of the swim bladder works very well. Basically, you stick a needle in the swim bladder and suck out some of the air. Not something to be entered into lightly, but does work well. This is not a cure, but a successful treatment. The head veterinarian at the Baltimore Aquarium prefers this method.
- 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.
DISCLAIMER: The opinions expressed herein are nobody's but my own. Please don't sue the University, the Vet School, or me for that matter, if you still have problems after reading this.
I am speaking for nobody but myself in writing this: The University of Pennsylvania School of Veterinary Medicine has nothing to do with my dissemination of this information, so please don't sue them (or me, for that matter) if you still have trouble treating ich after reading this.
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