1. Passive acoustic monitoring (PAM) is a non‐invasive technique that uses hydrophones to monitor populations and ecosystem dynamics. Although many applications of PAM have been developed in recent years, it has never been used to identify a calling marine species. 2. The south pass of Fakarava Atoll, French Polynesia, hosts spawning events of many reef fish species, including the camouflage grouper Epinephelus polyphekadion, with a spawning aggregation abundance exceeding 17 000 individuals during the full moons of June and July. 3. The current study aimed to use PAM to distinguish camouflage grouper sounds among the vocal activities of all fish recorded during the aggregation periods. Audio recordings analysis resulted in the identification of 29 sound types, some of which showed diel and lunar patterns. 4. Temporal analysis of these sounds in relation to spawning activities allowed the identification of camouflage grouper calls. These calls can be described as a single pulse or a series of ‘boom(s)’ with a pulse duration of ~44 ms and a low dominant frequency of 103 ± 31 Hz. Video recordings show that the camouflage grouper produces the ‘booms’ to initialize spawner ascent and to promote synchronous gamete release into the water column. 5. The study highlights for the first time that PAM can be used to identify the previously unknown sound of a fish species. Moreover, we can use it to understand the phenology of some biological activities for improving the resolution of fish biodiversity assessments.