Ecological and life history characteristics of ruffe (Gymnocephalus cernuus) in relation to other freshwater fish species

Ecological and life history characteristics of ruffe (Gymnocephalus cernuus) were studied in relation to 33 other native freshwater fish species in Finland. The descriptive ecological characteristics included 1) trophic guild, 2) species interaction. 3) adult habitat, 4) spawning habitat, 5) reproductive behavior, and 6) reproductive guild. The life history variables included 1) age at maturity, 2) length at maturity, and 3) fecundity as a number of eggs. Three different clusters of fish species were found in cluster analysis based on the ecological characteristics. The most distinct cluster of 7 species was comprised of predators. Ruffe was grouped into the largest cluster together with 20 other species and was closest to the cyprinid. gudgeon (Gobio gobio). In multidimensional scaling species were placed in two hypothetical dimensions firstly by their interaction with other species, trophic guild and adult habitat and secondly by their spawning habitat. Ruffe was placed near the center of the plot, suggesting that it has no special ecological requirement among the characteristics and species studied. Subsequent analysis of the life history characteristics revealed that ruffe was similar to the most typical r-selected species in Finland, showing high fecundity and low length at maturity, but with slightly slower growth rate. We, therefore, concluded that adult ruffe is a potential invader species showing no special ecological requirements and with life history characteristics typical for r-selected species.