Shared Call Structure and Fine-Scale Spatial Variation in Calls Attributed to Boesemania microlepis in the Cambodian Mekong River

Passive acoustic monitoring supports studies of fish activity and habitats in changing tropical rivers, yet cross-site consistency and local variation in calls remain poorly quantified. We monitored four sites (West, Middle, East, and Dock) across approximately 2 km of the Kampi reach of the Cambodian Mekong River. Automated detection and manual review were combined with fish surveys, hydrological observations, and background sound measurements. Published acoustic features and captures at the study sites supported attribution to Boesemania microlepis. At all sites, calls shared pulsed, harmonic structure, with site-median harmonic spacing of 114.8–119.1 Hz; 77.3–94.2% occurred at 16:00–20:00 local time. Rates of confirmed received events across daytime and nighttime recordings were 2.32–6.06 calls per minute of valid recording. Date-paired comparisons showed that Dock’s 95% cumulative-energy frequency was 200.0–235.1 Hz lower than at the other sites. Within-sequence call repetition rates at East were 0.327 and 0.241 calls/s lower than at West and Middle, respectively (Holm-adjusted p < 0.05). Dock’s lower-frequency spectrum coincided with deeper surrounding water, whereas detection and repetition rates followed distinct site patterns. Shared structure and local variation provide a quantitative basis for cross-site identification and habitat monitoring that integrates call features, activity timing, and environmental conditions.