Most bony fishes, including those that dwell in the water column, possess an important organ with a number of important functions, among them are:

Buoyancy Control. The air bladder allows the fish to control its buoyancy so as to stay at a certain depth of the water column without expelling much energy.

Sound Production: The air bladder of some fish species could play the role as that of sound production associated with the drumming in some catfish.

Hearing: The air bladder could facilitate the amplification of sound waves, thus increasing the sensitivity of hearing in a fish.

Gas Exchange: The air bladder may supplement gas exchange in low oxygen-holding aquatic environments in some species of fish.

However, it is in itself a fact that all fishes do not possess this air bladder. Sharks and rays are examples of cartilaginous fish which do not have an air bladder. Other types of buoyancy, such as large oil-filled livers in these fish, serve for this purpose.

Conclusion The air bladder is very important in the evolution history of most species of fish. Through it, they have been able to travel and dwell quite effectively in any type of aquatic setting.