This study assessed fish diversity, assemblage structure, body condition, and conservation status in the Nam Lik River Basin, Hin Hurp District, Vientiane Province, Lao People’s Democratic Republic. Sampling was conducted twice at six sites, three along the main river channel and three in its tributaries, during June and July 2022. The objectives were to document species composition, describe distribution patterns, evaluate health status, calculate diversity indices and fishing effort, and provide baseline data to support conservation and sustainable fisheries management. A total of 2,062 fish specimens were collected, representing 38 species belonging to 19 families and 9 orders. Cyprinidae was the most species‑rich family (14 species), followed by Bagridae and Danionidae (3 species each), Mastacembelidae and Osphronemidae (2 species each), while the remaining families were represented by a single species each. Ecologically, habitat generalists (Group G5) were the most abundant, indicating high adaptability to varying environmental conditions. According to IUCN Red List criteria, most species were classified as Least Concern, with one species listed as Vulnerable and another as Near Threatened.
Biodiversity indices (Shannon H′ and Simpson 1‑D) ranged from 0.60 to 0.70, reflecting moderate to good diversity across the basin. The condition factor (K) varied from 0.18 in Xenentodon canciloides to 2.39 in Brachirus harmandi, with an overall median of 1.30 and site averages between 1.14 and 1.53. These findings confirm that the Nam Lik River Basin still supports a diverse fish community, though targeted habitat protection and long‑term monitoring is recommended to prevent future declines and maintain ecosystem integrity.