Conservational studies for the endangered species, Tribolodon nakamurai(Pisces, Cyprinidae) based on ecological surveys and genetic analyses of present populations.

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Tribolodon nakamurai is an endangered species distributed only in some rivers flowing to Sea of Japan in southern Tohoku District. Its behavior is unknown, because its population-density is extremely low in any habitats. In this study, we conducted ecological surveys for T. nakamurai and T. hakonensis as a control species in Mogami River Systems, Yamagata and Agano River Systems, Fukushima where Hanzawa and Taniguchi (1982) had ever investigated. Using living and dead samples, we also carried out feeding experiments and population analyses based on two different DNA markers, clarified its behavior and population structures, and estimated degree of emergency of extinction.Although some individuals of T. nakamurai could be collected in downstream of Mogami and upperstream of Agano Rivers, less individuals were confirmed in upperstream of Mogami River. In 2006 and 2007, no individual of T. nakamurai was observed in known spawning ground in the river, revealing that its spawning was inhibited by abnormal warm in the winters. Observation of living individuals showed that the species is a fish-eater, suggesting that the food habit is related to its extremely low population-density. Mitochondrial DNA analysis showed that Mogami and Agano populations are genetically differentiated and genetic diversity is considerably low in all populations. Similarly, microsatellite analysis showed that genetic diversity is remarkably low in all populations. The both analyses detected a hybrid between T. nakamurai and T. hakonensis from downstream of Mogami River for the first time. From these results, we concluded that 1) number of individuals of T. nakamurai considerably decreased in both present populations, 2) there is the possibility that their fitness has decreased by inbreeding and introgression, 3) Mogami and Agano River populations should be regarded as different conservation units, and 4) their spawning grounds and habitats should be immediately conserved.