The Swim Bladder

Not all fish have a functional swim bladder and some fish have developed different uses for theirs. But in most fish it is used to maintain neutral buoyancy so that the fish doesn't have to waste energy to maintain itself at the required level in the water. Some bottom living fish use their swim bladder to generate sound.

The swim bladder is a large gas filled organ with muscles attached so that it is able to expand an contract. In some fish there is a ducting system in place to allow the gas volume to be adjusted, in other fish there is no such system but the gas volume can still be altered because the gas can be exchanged through the blood of the fish.

In most fish it is a single chambered organ but in Carps it is double chambered, which is another reason that fancy Goldfish have so much trouble with their swim bladders. If one side becomes less well developed because of the radical changes made through selective breeding then the fish will have to expend a lot of energy trying to maintain its balance.

Some other fish like some species of Gobies that have taken to living on the bottom of fast flowing streams have small swim bladders that no longer function or they are absent altogether, because in this situation an active swim bladder could cause the fish to be swept away.

In most fish however it is a large organ and can form up to 7% of the fishes total volume.

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