# Spatial Organization of Fish Assemblages and Its Relation to Environmental Factors in the Lower Yalong River, China

## TL;DR

This study explores how fish species in the Yalong River region change based on environmental factors and river structure.

## Contribution

The study identifies distinct fish assemblage patterns across different river orders and links them to environmental variables.

## Key findings

- Fish species diversity peaks in mid-order rivers before declining.
- Key species turnover occurs from low- to high-order rivers.
- Water depth and turbidity are major factors influencing fish assemblage variations.

## Abstract

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. Totally, 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 water depth and turbidity. Moreover, this study highlights the critical role of mid‐order rivers in sustaining fish diversity within dendritic stream networks of mountain rivers.

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.