How important is the presence of air bladder in Pisces?

Air bladder in Pisces regulates buoyancy and helps in floating in the water. It prevents them from sinking,
(ii) Air bladder is present in members of the class Osteichthyes.
(iii) Animals of the class Chondrichthyes do not have air bladder and in the absence of air bladder, the animals have to,swim constantly to avoid sinking.