Fish

[fire]

A hollow, gas-filled balance organ that allows a fish to conserve energy by maintaining neutral buoyancy how dose this work and why do they have such a thing in them apart from it gives them energy and buoyancy is it used for any thing else

[Clanad]

Not all fish have one... those that don't have to contiously swim or sink to the bottom, which, as you probably already know, is the main purpose of the swim bladder. In some fish the air from the bladder can be used to make sounds. Here in the U.S. a popular smaller game fish caught from docks on the Gulf of Mexico is called the "croaker"... They can emit croaking sounds for up to an hour after being caught...