Fish Community Composition in the Emur River, a Tributary of the Upper Heilongjiang (Amur) Basin in China

This study investigated the fish species composition and environment of the Emur River, a tributary of the Upper Heilongjiang (Amur) River system, which is a typical extreme-cold region of China. From 2022 to 2024, 28 native species (27 species of fish and 1 species of lamprey), including 4 endangered species, were monitored from 14 sampling sites. When grouped according to the main stream vs. tributaries and summer vs. autumn, we found significant differences (p < 0.05) in the composition of the fish communities. In autumn, the main stream fish assemblage was dominated by common species that prefer a slow current, including Phoxinus phoxinus (33.7%), Lota lota (25.2%), and Phoxinus lagowskii (19.8%). The tributary fish assemblage was primarily composed of typical coldwater fish species, such as L. lota (48.9%), Cottus poecilopus (20.2%), and Thymallus grubii (18.1%). However, in summer, there was no significant difference between the main course and tributaries. Canonical correspondence analysis showed environmental factors, including water temperature, elevation, and dissolved oxygen, to have significant impacts on the fish distribution to an extent that varied with species. This study may contribute to the management of coldwater fish diversity in mountain rivers and the protection of aquatic species habitats in regions of extreme cold.