Implication of aggressive, submissive and reproductive sounds in the way of life of clownfishes

Clownfishes are brightly coloured coral reef fishes well known for their mutualistic symbiosis with tropical sea anemones. These fishes live in social groups in which there is a size-based dominance hierarchy. In this structure where sex is socially controlled, agonistic interactions are numerous and serve to maintain size differences between individuals adjacent in rank. Clownfishes are also prolific callers whose sounds seem to play an important role in the social hierarchy. Agonistic interactions being involved in daily behaviour suggest how important acoustic communication might be in their way of life.
Recording the different acoustic behaviours indicated that sounds are divided into two main categories: aggressive sounds produced in conjunction with threat postures (charge and chase), and submissive sounds always emitted when fish exhibited an appeasement display (namely the head shaking movements). Both types of sounds showed size-related intraspecific variation in dominant frequency and pulse duration: smaller individuals produce higher frequency and shorter duration pulses than larger ones. Consequently, these sonic features might be useful cues for individual recognition within the group. On the other hand, no acoustic call was associated with courtship and reproductive behaviours.
Unlike other pomacentrids, sounds are not produced for mate attraction in clownfishes but to reach and to defend their breeding status, which explains why constraints are not important enough for promoting call diversification in this genus. However, acoustic signals seem to be an integral part of the peculiar way of life of clownfishes, although they are restricted to agonistic interactions only.