Fish Sound Production: the Swim Bladder is not a Resonant Structure

In teleost fishes, the swim bladder is an organ filled with gaz that, in addition to providing buoyancy, plays a role in hearing and, in some species, in acoustic communication. Although several studies in different species have demonstrated that the swim bladder has a prominent role in sound production, its function in this process remains largely unknown in the absence of extensive studies on the subject. A first approach, borned in the 60's, considered the swim bladder as a « resonant bubble » which describes it as an omnidirectional resonant gaz bubble, i.e. an acoustic monopol. This theory has been rarely discussed even though litterature discribed, since then, an unusual high damping rate for a free bubble. Wrongly justified by the properties of the surroundings tissues, we show that this damping property is in fact an intrinsec property of the swim bladder, the organ fails to resonate. For the species with sonic muscles, sounds are more likely to be the result of a forced response to muscular contraction and should not be amplified at the eigenfrequencies of the swim bladder.