Social context shapes acoustic signalling in the territorial damselfish Stegastes fuscus.

Acoustic communication plays an important role in social interactions in reef fishes, but how signals vary with behavioural context remains poorly understood for many species. We characterised the acoustic repertoire of the Brazilian damselfish Stegastes fuscus using synchronised underwater audio-video recordings and tested how sound features vary across social behaviours. Sounds were recorded during agonistic and courtship-related interactions, and temporal and spectral acoustic parameters were measured to compare acoustic structure among contexts. Differences between behaviours were primarily found in temporal features: Courtship sounds were longer and contained more pulses than agonistic sounds. These results show that S. fuscus conveys social context mainly through modulation of temporal organisation rather than spectral properties. Our findings indicate that a single call type can be flexibly adjusted to signal behavioural context during territorial defence and courtship. By documenting the acoustic repertoire of a dominant territorial herbivore, this study highlights how social context structures sound production in damselfishes.