Between 1975 and 2021 the diversity of fish communities of mountain rivers was studied in seven areas of the river Amur drainage: “Onon”, “Upper Zeya”, “Upper Bureya”, “Upper Amgun”, “Lower Amgun”, “Khingan”, “Lower Amur and Ussuri”. In these areas, various reaches of typical mountain watercourses were surveyed: 1) upper reaches (24), 2) “middle” (17) and 3) “lower” (10); 9 small mountain tributaries of lowland rivers – Amur and Ussuri, 5 mountain lakes and 6 floodplain reservoirs. According to the results of the research, 6 main types of communities were identified, including river ones: 1) upper reaches, 2) “middle” parts, 3) “lower” parts, 4) small mountain tributaries of large lowland rivers. Lake communities are represented by two main types of communities: 5) mountain lakes and 6) floodplain water bodies. In river communities, 30 fish species and one lamprey species were found; river communities are dominated by Barbatula toni, Cottus szanaga, Brachymystax tumensis, species of the genus Thymallus, as well as Rhynchocypris lagowskii and Phoxinus phoxinus. Upper reaches communities include from 4 to 12–13 species. Barbatula toni, Cottus szanaga, Brachymystax tumensis, and species of the Thymallus dominate here. In the communities of the middle parts of the rivers, there are from 7 to 17 species. Up to 23 species and one lamprey species are found in the lower parts. In the upper reaches and middle sections of the rivers, the composition of the community changes during the year as a result of seasonal migrations. In communities of mountain lakes 6 species of fish were found; three species are most common: Barbatula toni, Cottus szanaga, Brachymystax tumensis. 8 species inhabit floodplain water bodies, dominated by Rhynchocypris percnurus, Perccottus glenii, Misgurnus mohoity. The specificity of the region's coenotic diversity is determined by its position in the Amur basin, the presence or absence of mountain and floodplain lakes, as well as geomorphological and paleogeographic features.