Abstract:

Aims: The Nujiang River is an important international river in Southwest China. It is known as one of the world’s biodiversity hotspots, and the region is rich in unique fish resources. Due to its geographical location and topographical conditions, there is a lack of systematic studies on the species diversity and distribution patterns of fish species in the Nujiang River Basin.
Methods: In this study, fish composition information of the Nujiang River Basin was systematically sorted out based on data from a five-year field sample of the river basin, as well as data from literature, books and online databases. The spatial distribution patterns of the Nujiang River Basin fish species were analyzed via clustering and ordination methods.
Results: The results revealed that there were 85 indigenous fish species in the Nujiang River Basin. These fishes belong to 5 orders, 12 families and 47 genera. There were also 18 exotic fish species that belong to 3 orders, 8 families and 16 genera, in addition, two exotic species were newly recorded by field investigation. The fish diversity in the Nujiang River Basin significantly increased from the upper reach to lower reach. According to the results of clustering and ordination analysis of fish composition, the 25 sub-basins of the Nujiang River can be divided into three parts: (1) The upper reach in the Tibet Autonomous Region, there were 15 species. Fish of Schizothoracine and Triplophysa were dominant species, indicating a typical fauna characteristic of cold-water fish in the Qinghai-Tibet Plateau. (2) In the middle reach from Gongshan to Lushui, there were 36 species. Aside from the cold-water fish species of the upper reach, fish of Barbinae and Labeoninae were also presented in this area. Fauna characteristics demonstrated the change from plateau fish species to plain fish species. (3) In the lower reach below Lushui, there were 74 species. Among them, the thermophilic fishes of Barbinae, Labeoninae, and Danioninae were widely distributed in the main stream, while a large number of Schistura and Glyptothorax fishes were more likely to be found in tributaries. The fish composition of this section has characteristics of tropical river and floodplain fauna. In recent years (2017-2021), several surveys have found only 43 native fish species together (50.6% of the historical records), and fishery resources in the Nujiang River Basin were decreasing significantly.
Conclusion: Overfishing, development of small hydropower stations in tributaries, and the invasion of exotic fish species were the main threats to the native fish of the Nujiang River Basin. With the rapid increase in human activities, fish in the Nujiang River Basin were greatly threatened. Thus, systematic management and conservation planning for fish resources at the watershed-level are urgently needed.

Key words: fish, species richness, diversity pattern, similarity analysis, Nujiang River, international river