Abstract
Genetic differentiation among 34 populations of the fluvial land-locked goby, Rhinogobius flumineus, endemic to southwestern Japan, was investigated by electrophoretic methods . Twenty-three loci, which were presumed to correspond to 15 enzymes and one non -enzymatic protein, were scored. Genetic differentiation within the species was high compared with other amphid romous or peripheral fishes, probably due to more restricted gene exchanges between adjacent populations.
From the allelic constitution, 5 population groups could be recognized. The largest group, distributed in the western part of Japan, included 21 populations with low genetic differentiation (mean genetic distance; 0.04). Six populations distributed in the eastern part of Japan, bounded by the Suzuka Mountains, constituted the second largest group (mean genetic distance; 0.02). The most divergent group, distributed at the eastern edge of the species' range, had a unique allelic constitution, not only when compared with other groups but also within populations of the group itself. The geographical patterns ofthe genetic groups were discussed in relation to the geological history of the Japanese Archipelago since the Pleistocene.
