Effects of fish size on agonistic sounds in the clownfish Amphiprion akallopisos : implications for the role of the swimbladder in the sound production mechanism?

Clownfishes (i.e. Amphiprion akallopisos) are territorial fishes that use sound production to defend their anemone territory. They live in social groups which display a size-based dominance hierarchy. In such a system, agonistic interactions are frequent and play an important role in the social organization. In addition, these interactions are often associated with sounds. In this study, we compared the sonic features between individuals of different sizes and in different sexual status (juvenile, male and female). The existent relationship between fish size and swimbladder size also implied to seek the swimbladder role in the sound production.
Sound analyses showed that juveniles, males and females had distinct sounds in the dominant frequency and pulse duration. These differences were however not in relation to the sexual state; influence of sex on sonic features being mainly the result of a size dimorphism between sexes. Differences in calls were therefore due to the respective size of the emitter. This observation highlighted the role of the swimbladder as a resonance chamber. This role was also reinforced because the experimental filling of the swimbladder with physiological liquid significantly modified the acoustic features.
In A. akallopisos, frequency and pulse duration are directly related to swimbladder size, and thus to fish size. This relationship provides strong evidence that the emitter could be identified by its calls.