The air bladders are more or less sac like structure lying between the alimentary canal and the kidneys and contain a mixture of carbon dioxide, oxygen and nitrogen. Generally, the gas bladder opens into oesophagus and it is present in all the osteichthyes, except a few.
The anterior part of the bladder whether open or closed is specialized for gas secretion, while the absorption of gas into the blood takes place in posterior region. Histological, the wall of the anterior chamber of a cyprinid bladder consists of the following:
Tunica External made up of collage-nous fibers
Submucosa of connective tissue
Lamina propria formed of connective tissue
Inner most layer of epithelial tissue
The gas bladder is usually connected with the internal ear. It is homologous with the lungs of Dipnoi, Teleostomi and tetrapodes. The dorsal respiratory diverticulum developed from the gut of ancestral fishes, which later give rise to air bladder of modern Teleosts.
Air bladder acts as a hydrostatic organ.
Gas secretion. If gas is removed fro the blade, again the gas is secreted. Generally fishes living in deeper wear, fill the gas bladder with O2.
Air bladder is also respiratory in function. It is also used to store) 2 for emergency.
It is sensory in function. When fish is subjected to pressure changes in different depths of water compression of air take s place and gives sensation accordingly.
It is auditory in function.
It is also a sound producing organ