Abstract :
[en] The /Kwa/ vocalization dominates the soundscape of Posidonia
oceanica meadows but the identity of the species emitting this
peculiar fish sound remains a mystery. Information from sounds
recorded in the wild indicates that the emitting candidates should be
abundant, nocturnal and benthic. Scorpaena spp. combine all these
characteristics. This study used an interdisciplinary approach to
investigate the vocal abilities of Scorpaena spp.; morphological,
histological and electrophysiological examinations were interpreted
together with visual and acoustic recordings conducted in seminatural conditions. All observed Scorpaena spp. (S. porcus, S. scrofa
and S. notata) share the same sonic apparatus at the level of
the abdominal region. This apparatus, present in both males and
females, consists of 3 bilaterally symmetrical muscular bundles,
having 3–5 long tendons, which insert on ventral bony apophyses of
the vertebral bodies. In all chordophones (stringed instruments), the
frequency of the vibration is dependent on the string properties and
not on the rate at which the strings are plucked. Similarly, we suggest
that each of the 3–5 tendons found in the sonic mechanism of
Scorpaena spp. acts as a frequency multiplier of the muscular bundle
contractions, where the resonant properties of the tendons determine
the peak frequency of the /Kwa/, its frequency spectra and pseudoharmonic profile. The variability in the length and number of tendons
found between and within species could explain the high variability of
/Kwa/ acoustic features recorded in the wild. Finally, acoustic and
behavioural experiments confirmed that Scorpaena spp. can emit the
/Kwa/ sound.
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