Abstract:

The Lancang-Mekong River is the longest river in Southeast Asia, and is one of the richest areas of freshwater biodiversity in the world. Because it is an international river through six countries and holds extremely high fish biodiversity, there is a lack of systematic understanding of freshwater fish diversity. Over the past two decades, this team systematically compiled a list of freshwater fish species in 32 sub-basins or tributaries in the upper and middle reaches of the Lancang-Mekong River. Now in this paper, the species composition and distribution of fish have been analyzed, and the species diversity of the upper and middle reaches of the Lancang-Mekong River has been evaluated using the taxonomic diversity index. The results showed that 745 species of freshwater fish were recorded in the middle and upper reaches of the Lancang-Mekong River. These fish belong to 229 genera, 63 families, 17 orders and 2 classes. Of these, 451 species of Cypriniformes fish accounted for 60.5% of the species. The taxonomic diversity index showed that, from the source to the middle reaches of the river, the taxonomic distribution of freshwater fish became increasingly more even, the relationships were increasingly further apart, and the fish diversity gradually increased. Cluster analysis (CA) and multi-dimensional scaling analysis (MDS) results showed that the 32 sub-basins could be divided into three groups (Jaccard similarity coefficient=8.69), and the analysis of similarity (ANOSIM) indicated that the composition of freshwater fish differed significantly between the groups (R = 0.877, P = 0.001). Similarity percentage analysis (SIMPER) results indicated that Cypriniformes and Siluriformes were the main fish that differed among the three groups, and the species composition of groups presented distinctive changes at the family and species levels with the altitude rising. With the rapid population growth and economic development of the countries in the river basin in recent decades, the fish diversity and fishery resources of the Lancang-Mekong River face serious threats. Thus, it is urgent that countries in the river basin cooperate and formulate a scientific protection plan at the basin scale.

Key words: Lancang-Mekong River, freshwater fish, species composition, taxonomic diversity