How important is the presence of air bladder in pisces?

Question

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Answer 1

It is extremely useful for buoyancy control under the water.  By adding gas to the swim bladder, the fish can become more buoyant, and removing gas makes the fish less buoyant.  The fish can carefully adjust its buoyancy to allow it to remain at a constant depth easily.  

Scuba divers use this same principle when they add air to or release air from their buoyancy compensator jackets.  These devices get air from the scuba tanks, and the diver uses a button and a valve to add or release air.  With practice, a scuba diver can easily remain at a chosen depth by controlling the air in his buoyancy compensator.

Answer 2

Contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend, or descend without having to waste energy in swimming.