The purpose of this paper is to analyze the taxonomic structure and ecological indices of the fish communities in two types of aquatic ecosystems separated by the Dubasari Dam. The carried out research revealed a richer specific diversity and significantly higher quantitative values   of fishing communities in the downstream area of   the hydro power plant. The decisive factor is the fragmentation of the Dniester River, causing the interruption of reproductive, trophic and winter migration of reobionticfish species.