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Purpose. To determine the current species composition of fish and analyze the structure of ichthyofauna of the Stryi River catchment on the basis of field studies, published works and survey data.Methodology. Ichthyological studies were carried out in 2017-2019 on the Stryi river, as well as its tributaries Rybnik, Zubrytsya, Skhidnytsia and Opir. Adult fish were caught using hook and line gear and hand nets, the larvae and fry were collected using sweep nets and plankton nets. Species identification and morphological analysis of fish were performed according to standard methods. Incomplete biological analysis of most fish, including all individuals of the Red book species, was carried out in situ, with fish being subsequently released in the river.Findings. The data obtained indicate that at least 27 fish species belonging to 8 families are present in the Stryi river. The typical riverine (rheophilic) species predominate in fish fauna. The limnophilic species in conditions of mountain river are rare, and the distribution of invasive species is limited for now. Ichthyofauna of the Stryi has features of endemism and relictism. 6 species are listed in the Red Book of Ukraine, 10 are in the Berne Convention. Most fishes carry out long-range migrations within the main channel as well as its tributaries. In order to preserve native riverine ichthyofauna, in particular the rare fish species, it is necessary to carefully approach any economic activity within the river basin which disrupts the natural hydrological regime or leads to water pollution.Originality. For the first time, a comprehensive study of fish fauna in the Stryi River was conducted, the distribution of rare and endangered as well as invasive fish species, was analyzed.Practical value. The data obtained are necessary for planning measures for the protection of rare and endangered fish species and for the regulation of recreational fisheries. The results of this study were used as a part of the environmental impact assessment of small hydroelectric power plants construction on the Stryi River. Information on the ichthyofauna composition, the distribution of rare and endangered fishes, particularly those, which undertake spawning migrations, is important for consideration when planning any economic activity that disrups the morphology and hydrological regime of the river bed (gravel extraction, bank stabilization, damming etc.).