Agonistic sounds in the skunk clownfish (Amphiprion akallopisos) : spectral and temporal basis for fish size assessment and individual recognition

Clownfishes (i.e. Amphiprion akallopisos) are territorial fishes that use sound production to defend their anemone territory. They live in social groups within which there is a size-based dominance hierarchy. In such a system, agonistic interactions are usual and play an important role in social organization by maintaining size differences between individuals adjacent in rank. Sounds are known to be used in agonistic interactions; they could therefore be associated with aggressive display within the group hierarchy. In the present study, we compared the sonic characteristics between individuals of different sizes and of different sexual status (non-breeder, male and female).
Sound analysis revealed that dominant frequency and pulse length are highly correlated with fish size, and are not related to sex. No information related to size can be extracted from the pulse period, interpulse duration and number of pulses per train.
Evidence is provided that dominant frequency and pulse length are morphologically determined signals related to fish size. In that case, smaller individuals produce shorter duration and higher frequency sounds than larger individuals. Both sonic features are signals conveying information related to the size of the emitter. This finding could be of significant importance, and might help to understand one of the mechanisms that carry the clue for individual recognition within the group hierarchy.