Biological characteristics of the ruff (Gymnocephalus cernuus (L)) indwelling Karelian lakes

Results of the study (1996-2010) on the ruff (Gymnocephalus cernuus (L)) indwelling the Onega Lake (Lakhtinskaya Bay, Kondopozhskaya Bay), Pertozero, and Konchezero lakes are presented. The age, the size, the gender, and the weight composition of the ruff’s populations were indenified. In Lakhtinskaya Bay of Lake Onega, the ruff with less biomass and with a higher number of macrozoobenthos has bigger length, weight, and population increase than in Kondopozhskaya Bay (area Tulguba). This phenomenon can be conditioned by the presence of the functioning trout farm located in Lakhtinskaya Bay, i.e by the artificial trout feeds, which are not eaten by farmed trout. A stable numerical strength in ruff population of Pertozero and Konchezero lakes was observed, but under favorable conditions the fish population can quickly increase in number. A need to regulate the fish numerical strength is proven, and a set of necessary measures instrumental in numerical strength regulation are offered.