FISH SPECIES COMPOSITION AND SPATIAL DISTRIBUTION IN THE PHAN RIVER, LAM DONG PROVINCE, VIETNAM, DURING THE 2025 DRY SEASON

Abstract

This study investigates the species composition and spatial distribution of fishes in the Phan River basin, Lam Dong Province (formerly part of Binh Thuan Province) during the dry season from February to April 2025. Fish specimens were systematically collected at three representative sites corresponding to the upper, middle, and lower reaches of the river, in conjunction with measurements of environmental parameters such as salinity and pH. The results identified a total of 92 species, belonging to 77 genera, 57 families, 24 orders and 2 classes. The occurrence of the class Elasmobranchii and numerous marine families within the order Perciformes reflects the distinctive estuarine ecosystem of the lower reaches, where freshwater, brackish, and migratory marine fishes converge. The distribution of species among orders exhibited marked unevenness, with certain orders dominating in species richness, while many others contributed only a limited number of species. The order Perciformes was the most species-rich, comprising 18 species (19.57%). This was followed by the orders Carangiformes and Cypriniformes, each represented by 11 species (11.96%). In terms of spatial distribution, the fish populations of the Phan River are distributed as follows: in the upstream and midstream sections exhibited similar species compositions, with 28 species (30.43%) recorded in both areas, indicating that species inhabiting the upstream can also live in the midstream. The highest species richness was observed in the estuarine zone, with 64 species (69.57%). The survey also recorded several fish species listed in the Vietnam Red Data Book (2007) and the IUCN Red List (2025), underscoring the biodiversity value and the importance of conserving aquatic resources in this region.