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Abstract

Population genetic structure and migratory history of the common freshwater goby Rhinogobius sp. LD in the Shigenobu River system were surveyed by using three microsatellite loci and otolith Sr Ca ratio, to examine effects of two types of dams, a single dam with a reservoir Ishite-gawa Dam and multiple erosion-control dams without reservoir. Genetic variabilities were high in the Shigenobu River populations and the estimated hetero zygosity ranged from 0.843 to 0.889. Considerable genetic differences were observed between populations above Ishite-gawa Dam two sites and populations of the other nine sites above multiple erosion-control dams , within which the genetic heterogeneity was not observed. These results suggested that the populations above Ishite-gawa Dam were landlocked and differentiated genetically by the dam, whereas the goby populations were not isolated by multiple erosion-control dams. This was supported by the otolith Sr Ca analysis, which indicated that the goby individuals sampled from the sites above the Ishitegawa Dam had not experienced saltwater whereas those above multiple erosion-control dams had experienced. In addition, Sr Ca analysis suggested that a population just below the Ishitegawa Dam consisted of both landlocked drifted from the reservoir and sea-migratory individuals.