The swim bladder, gas bladder, fish maw or air bladder is an internal gas-filled organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth without having to waste energy in swimming. The swim bladder is also of use as a stabilizing agent because in the upright position the center of mass is below the center of volume due to the dorsal position of the swim bladder. Another function of the swim bladder is the use as a resonating chamber to produce or receive sound.
The swim bladder is evolutionarily homologous to the lungs. Charles Darwin remarked upon this in On the Origin of Species.
Read more about Swim Bladder: Fish Maws, Species, Structure and Function, Evolution, Human Uses, Similar Structures in Other Organisms
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