1. Tasty – In certain Asian cultures the swim bladders of large ocean fish are considered a tasty foodstuff, renowned as a delicacy that is commonly served braised.
2. Origin – Charles Darwin wrote: “There is no reason to doubt the swim bladder has been converted into lungs [and that] all vertebrates with true lungs are descended from an ancient prototype.”
3. Hearing – In some fish the swim bladder is connected to the labyrinth of the inner ear by a bony structure from the vertebrae. This provides a precise sense of water pressure and hearing.
4. Gas – The mix of gases in swim bladders varies. Shallowwater fish bladders tend to approximate that of Earth’s atmosphere, while deep-sea fish have higher oxygen mixes.
5. Bladder-free – Cartilaginous fish like sharks lack both lungs and swim bladders. This has led to postulation that both these organs developed 420 million years ago after such species divided from other fish.