Spatial organization of fish assemblages and its relation to environmental factors in the lower Yalong River, China

Based on data collected from 31 sampling sites during June and August 2018
in the three ordered rivers (the tributaries of the Anning River, the
Anning River, and the lower Yalong River), fish assemblages in the region
were investigated regarding their spatial variations, and their
relationship with environmental factors. In total, 48 species were
collected, with 47 being native and one being exotic. Among them, one was
classified as endangered. Fish species diversity increased first and then
decreased, reaching its peak in the mid-order river. Obvious variations
were found in fish assemblages depending on the stream order. There were
three site-groups: one covering the tributaries of the Anning River, one
covering the Anning River, and one covering the lower Yalong River. From
low- to high-order rivers, the alterations of key species within the fish
communities exhibited a turnover pattern. The fish assemblages in the
low-order river were primarily dominated by Nemacheilida, whereas the
mid-order river and the high-order river displayed a dominance of
Gobioninae and Cultrinae, respectively. These spatial variations might be
primarily impacted by altitude and water depth. Moreover, this study
highlights the critical role of mid-order rivers in sustaining fish
diversity within dendritic stream networks of mountain rivers.