Agonistic sound production by the frillfin goby ( <i>Bathygobius soporator</i> ) from southeastern Brazil

Bathygobius soporator is a benthic, site-attached gobiid species that predominantly inhabits intertidal rock pools and oceanic island habitats across the Atlantic. It was the first gobiid species for which acoustic signalling was formally described, with the known repertoire limited to male courtship displays. This study presents the first characterisation of agonistic acoustic signalling in B. soporator. Acoustic data were collected through audio recordings performed under controlled laboratory conditions. A total of 120 acoustic signals were recorded during dyadic interactions between males, comprising 109 ‘single pulses’, nine ‘double pulses’ and three ‘pulse trains’. Single pulses had an average duration of 8.6 ms and ‘double pulses’ of 167 ms, while pulse trains spanned up to 1552.1 ms in duration. These findings expand the known acoustic repertoire of B. soporator beyond courtship-related signals and demonstrate the production of vocalisations in agonistic contexts, suggesting a broader communicative function for acoustic signalling in this species.