A morphometric study on four land-locked salmonid species

Lakes in Vuoksi drainage area in eastern Finland are inhabited by four salm onid species: the grayling (Thymallus thymallus), the Atlantic salmon (Salm o salar m. sebago), the brown trout (Salmo trutta m. lacustris), and the ar ctic charr (Salvelinus alpinus). We studied second-generation hatchery-rear ed juveniles of these freshwater salmonids from two age groups: (0+)-year-o ld fish, and (1+)-year-old fish; and compared their morphology in order to assess both intra- and interspecific variation in morphometric characters, and changes associated with growth. We observed that the (0+)-year-old salm onids are morphologically very similar, but as they grow, the interspecific differences become more pronounced. The characters that best discriminate among the studied species are body height and head dimensions as well as pe ctoral fin length. The grayling and the arctic charr are streamlined, where as the salmon and the brown trout are more robust in their body shape. The shape of the studied species reflects also their adaptation to their native habitats.