Features of the ichthyofauna of freshwater bodies in 22 river basins of the northeastern Fennoscandia (Barents and White Sea basins, 1972-2024 studies)

The data on the distribution of fish species in 128 different types of freshwater bodies of northeastern Fennoscandia (Murmansk region, northern Karelia, northeastern Finland and Norway) (hereinafter referred NEF), belonging to 22 river basins (Barents and White Sea basins) for the time period from 1972 to 2024 are summarized. The factors determining the presence/ absence of fish species were analyzed. The trends of changes in the structure of fish communities of freshwater bodies under conditions of environmental changes were studied. The data are presented on the distribution and biological characteristics of the European whitefish Coregonus lavaretus, which remains a widespread species in various freshwater bodies of the NEF and often forms the “core” of their ichthyocenoses. In total, 20 species of fish live in the freshwater bodies of the study area, of which 16 are native and 4 are introduced. The basis of the native ichthyofauna of water bodies is the cold-water adapted group of fish. The number of fish species in a water bodies varies from 1 to 18. The distribution of fish species is determined by a number of factors, including geography, catchment area size, and water body morphometry. The number of species in the basins of medium-sized rivers of the Murmansk region increases in the direction from northwest to southeast due to taxa of higher rank (families and genera). The large and deep-water lakes and lake reservoirs of the White Sea basin are home to virtually the entire spectrum of species in this study area. The most common fish species are the Eurasian minnow, nine-spined stickleback, northern pike, burbot, European perch and European whitefish. It was established that in the studied water bodies the European whitefish is represented by various sympatric ecological morphs. The studied morphs of whitefish in the water bodies of 8 river basins of the NEF differ not only in the structure of the branchial apparatus and nutrition, but also in the age, growth and maturation of the fish. Differences in the structure of whitefish populations are observed both between water bodies of different river basins and within the basins of these rivers. In the studied water bodies of the NEF, a general tendency of transition of whitefish-salmon water bodies to whitefish-perch or whitefish-smelt water bodies is observed. These successional processes are associated with changes in fish habitat conditions under the influence of global and regional factors: climate change, hydropower, anthropogenic pollution, eutrophication, and invasive species.