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

Abstract

This study investigates the fish species composition and spatial distribution 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 estuary 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 Elasmobranchii and numerous marine families within Perciformes reflects the distinctive estuarine ecosystem of the estuary, 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. Perciformes was the most species-rich order, comprising 18 species (19.57%), followed by Carangiformes and Cypriniformes, each with 11 species (11.96%). In terms of fish distribution within the river basin, the upstream and midstream sections exhibited similar species compositions: 28 species (30.43% of the total) were recorded in both sections, indicating that species occurring upstream can also inhabit the midstream. The highest species richness was observed in the estuary, 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.