“My betta has swim bladder!”

Yeah, but does it? You can’t always use a goldfish diagnostic chart when trying to diagnose a betta fish.

Physostomes

Goldfish are physostomes, which means that their swim bladder is attached to their mouth.

A goldfish’s swim bladder can get easily overinflated due to feeding at the surface, which causes a positive buoyancy issue.

Sometimes constipation will prevent the fish from being able to deflate the swim bladder. Especially some fancy goldfish will have a small and very centrally located swim bladder where very precise inflation is necessary to maintain balance.

Normally though, a physostome can dynamically change the amount of air in its swim bladder to control its buoyancy at will.

Physoclisti

Betta fish are physoclisti¹, which means that their swim bladder is not attached to their mouth. The bladder is inflated through a complex system connected to the heart. The bladder can be reinflated if deflated due to injury or illness, but it happens very slowly, and in general, can not be inflated or deflated at will.

Positive Buoyancy Issues

If your betta is having problems where he’s floating and can’t submerse it’s likely that he has air trapped, but it’s likely going to be trapped in his stomach or intestines. It could still be related to an issue with eating, but often gas bubbles will be the result of bacteria giving off gas that collects in the GI tract.

Negative Buoyancy Issues

An infection to a swim bladder can cause it to deflate, especially in an asymmetrical way, as the infection may attack just one side of the swim bladder, causing a change to its shape. This will obviously be a systemic infection, and not an external one. It is possible to treat the infection and have the swim bladder reinflate over time. However, sometimes the damage will be done to the connective circulatory system, leaving it partially inflated or completely deflated.

Additionally, a swim bladder can rupture due to injury.

Sliders

Sliders are the name given to young betta where the swim bladder never inflates correctly.² They can live a normal life but are often culled.

If you adopt a slider or if your betta becomes a slider due to infection or injury to its swim bladder, they will enjoy a bare bottom tank so that they can “slide” instead of swim around. In a bare bottom tank, if you want a biological filter, you’ll want to purchase a pump filter with a biological filter section.

Literature Cited

¹ Regan CT. The Asiatic fishes of the family Anabantidae. Proceedings of the Zoological Society of London. 1910;1909:767–787. doi:10.1111/j.1469-7998.1910.tb06972.x

² Lucas GA. A study of variation in the Siamese Fighting Fish, Betta splendens, with emphasis on color mutants and the problem of sex determination. ; 1968.