Features of lake fish feeding near trout cages (the case of the Republic of Karelia)

The article presents a comparative analysis of lake fish (perch, roach, ruff and bream) nutrition near trout farms in the Republic of Karelia. The study revealed that in the cage zone, the diet of some fish changes significantly. It was established that in Lake Vokhtozero (during the open water period from 2013 to 2015) and in Kondopoga Bay of Lake Onega (in 2016) perch switched from traditional consumption of zooplankton and zoobenthos to feeding on small aboriginal fish floating near the cages in large quantities, which significantly increased fish stomach fullness. In Lake Vokhtozero, trout feed washed out of the cages by the current also was an additional source of food for perch and roach. Thus, it was the first study on Russian water bodies to establish that this kind of anthropogenic influence significantly changes the food chains of natural ecosystems.