This paper describes spatial and seasonal variation in fish assemblages by analyzing one year of daily fish catch data sampled at 32 sites covering Cambodia’s main inland water bodies. The authors recorded 125 fish species. Four clusters were distinguished based on assemblage composition similarity, and 95 indicator species were identified to characterize each of the identified assemblage clusters. High diversity fish assemblages were associated with the upper Mekong system and Mekong/Bassac/Tonle Sap Rivers in Kandal Province and southern Tonle Sap Lake while lower diversity assemblages were observed in the Mekong River in Kratie and the northern area of the Tonle Sap Lake. They find significant variation in the assemblage composition between wet and dry seasons, indicating strong seasonal species turnover within clusters. Length–weight relationship analysis indicated a negative allometric growth among a majority of indicator species, reflecting suboptimal conditions for growth. The study establishes contemporary structure and diversity patterns in the Lower Mekong River system of Cambodia, which can be used to map fish biodiversity hotspots and assess key indicative fish stocks’ statuses for conservation and management.

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