Nuon V. auteur aut IRD Chea R. auteur aut IRD Hugueny Bernard auteur aut IRD Grenouillet G. auteur aut IRD text journalArticle eng text/pdf reformatted digital access The Mekong River faces increasing environmental threats. To understand fish community responses to these threats, we explored the links between functional diversity (FD) dynamics and environmental changes across four sites using trait-based methods and fish monitoring data for 347 species. We assessed functional richness (FRic) and divergence (FDiv) using standardized effect sizes to investigate the main assembly rules structuring fish communities and used generalized additive models to identify key environmental drivers. After dam construction, all four sites experienced significant changes in environmental conditions. Deterministic processes, particularly environmental filtering, dominated in structuring fish communities. The upstream Lao People's Democratic Republic site (LPB) influenced by deterministic and stochastic processes. The Cambodia sites in Stung Treng province (CST) and Tonle Sap (TLS) Lake primarily driven by deterministic process with a decline in FRic and FDiv. Conversely, the Viet Nam site (VCM) seemed primarily influenced by stochastic process with more subtle environmental effects, evidenced by an increase in FRic and FDiv over time. The upper sites (LPB, CST, and TLS) displayed a distinct seasonal pattern in FD indices, with values decreasing during the dry season and increasing during the wet season. Conversely, the lower site (VCM) exhibited the opposite. Water level emerged as the key driver across all sites, with temperature and total nitrogen as secondary drivers. Dam impacts and other anthropogenic factors not included in our analyses (e.g., unsustainable fishing and habitat degradation) probably contributed to the observed changes in FD at specific sites. These findings highlight potential strategies for conservation, offering national and regional practitioners an opportunity to develop and refine river management plans. specialized Mekong River Community assembly Functional richness Functional divergence Freshwater fish Environmental change LAOS CAMBODGE VIET NAM MEKONG COURS D'EAU 036 034 380 125138 [11 p.] 2025 0301-4797 https://www.documentation.ird.fr/hor/fdi:010093358 10.1016/j.jenvman.2025.125138 0301-4797 [F B010093358] https://www.documentation.ird.fr/hor/fdi:010093358 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2025-05/010093358.pdf IRD - Base Horizon / Pleins textes 2025-05-14 2025-05-14 fdi:010093358 fre