The phylogenetic relationship and distribution of indigenous freshwater fishes in the Mekong tributaries, Vietnam

Abstract

The investigation of the biodiversity conservation along river catchments is a cost-effective nature-based solution to ensure the availability and sustainable management of water and the richness of biodiversity for all, with many co-benefits for the other sustainable development goals. The need for further exploration and conservation assessments of inland freshwater fish fauna coincides with expanding threats to freshwater resources from flow alteration and water diversion, increased sediment load, introduced species, overfishing and habitat loss. Meanwhile, former studies on the taxonomy of freshwater fish fauna of the Mekong tributaries in Vietnam were ambiguous and did not afford the phylogenetic relationships and geographic distribution. Our surveys from 2011 to 2021 on revising the indigenous fish fauna provided these phylogenetic relationship and geographic distribution. The evolutionary and phylogenetic relationships were analyzed for fish species by using several mitochondrial and nuclear genomes as COI, Cyto b, 16S rRNA, ATPase 6-8, RAG1, and delineated factors of fish distribution were also inferred. A total of 200 indigenous species belonging to 119 genera, 36 families, 11 orders were identified from 680 specimens collected at 18 sampling sites. Cypriniformes with 125 species (62%) and Siluriformes with 40 species (20%) were the most diverse orders. This study updated the scientific names with the correction of one species and the determination of the phylogenetic relationship. The endemism integrated from this study and the modified global fish phylogenetic data. The Mekong tributaries of Vietnam possessed 73 endemic species, withholding 36% of the total studied primary species. In terms of each ecoregion fauna, the proportion of the Mekong endemics was much higher than those in Nam Neua river (46%), 3S rivers (27%), and Se Pon river (25%). Based on their zoogeography, the studied fishes were subgrouped into three units: 43 species of Lower Langcang, 32 species of Khorat Plateau and 177 species of Kratie‒Stung Treng.