ECOLOGICAL AND LIFE-HISTORY CHARACTERISTICS OF RUFFE (GYMNOCEPHALUS-CERNUUS) IN RELATION TO OTHER FRESH-WATER FISH SPECIES

Ecological and life history characteristics of ruffe (Gymnocephalus ce rnuus) were studied in relation to 33 other native freshwater fish spe cies 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 lif e history variables included 1) age at maturity, 2) length at maturity , and 3) fecundity as a number of eggs. Three different clusters of fi sh species were found in cluster analysis based on the ecological char acteristics. The most distinct cluster of 7 species was comprised of p redators. 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 di mensions firstly by their interaction with other species, trophic guil d 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, s howing high fecundity and low length at maturity, but with slightly sl ower growth rate. We, therefore, concluded that adult ruffe is a poten tial invader species showing no special ecological requirements and wi th life history characteristics typical for r-selected species.