One synonym for "gas bladders" is "swim bladder", which is an organ found in many fish that allows them to adjust their buoyancy in the water. Other synonyms include "air bladder", "pneumatic sac", and "float bladder". These organs work by filling with gas, usually oxygen, which helps the fish control their depth in the water. Some fish species also use their swim bladder to produce sounds or vibrations for communication or navigation purposes. While gas bladders are common in fish, they are not found in all species and can vary in size and shape depending on the fish's environment and lifestyle.