Sea, sound and sun: bioacoustics of triggerfishes (Balistidae)

Triggerfishes (Balistidae) are common fishes of shallow tropical waters that are known to produce
sounds. We described these sounds in Rhinecanthus aculeatus as a series of pulses that result
from alternate sweeping movements of the right and left pectoral fins, which push modified scales
that are forced against the swim bladder wall. Pulses from each fin occur in consecutive pairs. Highspeed
videos indicate that each pulse consists of two cycles: the first part of each one corresponds
to the inward buckling of the scutes, whereas the second part of the cycle correspond to an apparent
passive recoil of the scutes and swim bladder wall.
More recently, we show that the sound production mechanism is similar in others Balistidae species.
According to recent phylogenetic data and shared morphological features, this mechanism could be
common to the majority of Balistidae family members. In the sister family (Monacanthidae), similar
morphological features have not been described and sounds resulting from pectoral fin movements
have not been reported. Therefore, we can reasonably argue that the detailed sonic mechanism
using pectoral fins, scutes and the swim bladder could be a strong Balistidae feature. It could have
evolved from locomotory movement and be a new example of exaptation.