Male fish often use the swim bladder as a specialized resonating organ for drumming calls.
Many vocal fishes produce sounds by contracting muscles attached to, or located near, the swim bladder. The bladder is a gas-filled structure whose vibrations can be amplified and radiated into the surrounding water. In several fish groups, males use these sounds during courtship, spawning, or territorial interactions.
The exact mechanism varies among species. Some fishes have sonic muscles that beat rapidly against the bladder, while others make sounds by rubbing bones or moving body structures. Therefore, the swim bladder is an important sound-producing organ in many fishes, but it is not the sole mechanism used by all vocal species.
A swim bladder also helps many bony fishes control buoyancy. Its role in sound production is an additional evolutionary use, not its universal primary function. Sharks and rays, which lack a typical bony-fish swim bladder, use different sensory and acoustic adaptations.