Anatomy of finfish and shellfish

Unit 6 - Respiratory system in fishes

6.3.1.Functions of Air bladder or Gas bladder
As a Hydrostatic organ: It is important function of air bladder is hydrostatic. This is because of the fact that the bony fish can fill up or empties the bladder at will. This help them to maintain their body density closely to that of the surrounding environment thus the air bladder actually act as “float” in the body cavity. When the gas content in the bladder is increased, the fish becomes lighter and it rises to higher levels and conversely when diminished the fish sinks deeper in water.
As a respiratory organ: fishes which have to live in draught condition or foul water, the bladder sometimes acts as a subsidiary or accessory respiratory organ. In some deep water marine fishes the air bladder acts as a store house of oxygen. In some gill breather also store or in their air bladder for emergency purpose.
As a sound, producing organ: A large number of fish species uses the air bladder for sound production. By producing characteristics sound, the fish probably communicates with the apart sex. Sound is also produced when fish “apprehends any danger”.
As a sensory organ: It is viewed that the wall of the air bladder is highly sensitive to water pressure as well as temperature fluctuations. Thus air bladder acts as a barometer or monometer or a Hydrophone.