Fish community structure in mainstream of lower reaches of Jinsha River (Shuifu-Yibin section)

The lower reaches of the Jinsha River (Shuifu-Yibin section), a nursery habitat for various rare and endemic fish species of the Yangtze River, are one of the areas with dense construction of large hydrop projects. However, the fish biodiversity in this region is under severe threat. To assess the status of its fish resources, we had conducted ten surveys from 2021 to 2023 in three river sections: Anbian Town, Sankuashi and Baixi Town. The results show that a total of 69 fish species belonging to 8 orders, 20 families and 50 genera were collected, with the Cyiformes being the most abundant (48 species). There were 17 endemic fish species from the upper Yangtze River, 7 species of nationally protected wildlife, and 8 invasive species. The dominant species in the community included Coreius heterodon, Tachysurus vachelli, and Leiocassis crassilabris. Among the biodiversity indexes, only the Margalef richness index showed significant temporal and spatial differences (p<0.05). The ABC curve indicates that the fish community was in a state of moderate disturbance, but with a trend of increasing dominance of larger individuals. Cluster analysis shows that at a similarity level of 56.71%, the species from 2021 and 2022 were grouped together due to their similarities, while the ones in 2023 were more similar to historical records so they were grouped together. Compared with the results from 2021 to 2022, there had been an increase in fish species in the mainstream of the Jinsha River (Shuifu-Yibin section) in 2023. It is recommended that measures such as continuous fish stocking, controlling the invasion of non-native fish species, and strengthening scientific monitoring be implemented to further promote the recovery of fish populations in the Jinsha River and the Yangtze River.