Although the fishes' swim bladder is primarily an organ for buoyancy control, it also functions in the production and generation of sound. Many fish, particularly those of coastal waters, have muscles that insert into the swim bladder. When the muscles are contracted, the swim bladder vibrates, producing a hollow-like sound. These sounds have been described as grunts, groans, thuds, and barks. Some species, like croakers, make sounds at feeding times, while others make noise during reproductive periods.
The swim bladders of fish can also act as a receptor of sound--one even better than their own ears! Swim bladders can discriminate a wider range of frequencies, can better determine pitch, and are more sensitive to sound than the bony otolith of the ear. Most fish have some kind of connection between the inner ear and the swim bladder.
Using the SOFAR channel, a low-velocity zone of sound near the base of the thermocline (the buffer zone between the upper layer of water and the frigid layer below), animals can transmit sounds for great distances.
Go to marine mammal acoustic article.
Go to hypertext article