Unusual sound production mechanism in the triggerfish Rhinecanthus aculeatus (Balistidae)
Résumé
The ability to produce sound has been known for decades in
Balistidae. Sounds of many species have been recorded and a variety
of sound-producing mechanisms have been proposed, including
teeth stridulation, collision of the buccal teeth and movements of the
fins. The best-supported hypothesis involves movements of the
pectoral fin against the lateral part of the swimbladder, called a
drumming membrane. In this study, we describe for the first time the
sounds made by the blackbar triggerfish Rhinecanthus aculeatus,
which are like short drum rolls with an average duration of 85 ms,
193 Hz dominant frequency and 136 dB SPL level at 3 cm distance.
The sounds are a series of pulses that result from alternate sweeping
movements of the right and left pectoral fins, which push a system of
three scutes that are forced against the swimbladder wall. Pulses from
each fin occur in consecutive pairs. High-speed videos indicate that
each pulse consists of two cycles. The first part of each cycle
corresponds to the inward buckling of the scutes, whereas the second
part of the cycle corresponds to an apparent passive recoil of the
scutes and swimbladder wall. This novel sound production
mechanism is probably found in many members of Balistidae
because these peculiar scutes occur in other species in the family.
Comparison of sound characteristics from fishes of different sizes
shows that dominant frequency decreases with size in juveniles but
not in adults.
KEY WORDS: Acoustic, Communication, Swimbladder