The sounds of bicolor damselfish (Pomacentrus partitus): Predictors of body size and a spectral basis for individual recognition and assessment

Evidence is provided that the ‘‘chirp,’’ a sound commonly produced by males of the bicolor damselfish (family: Pomacentridae) possesses an anatomical constraint: The peak frequency within its power spectrum reflects a clear inverse relationship to body size. For every 1-mm change in the standard length of a male (range: 50–69 mm), the peak frequency of its sounds shifts by approximately 20 Hz. The ultimate constraint appears to be the volume of an individual’s gas bladder. This provides an individualistic feature to the sounds of different sized colony members, all of whose sounds possess an otherwise extremely stereotyped temporal pattern of their included pulses. This finding may aid in clarifying the mechanism that provides the clue for the already established acoustical recognition of individuals within colonies of the species.