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

中村三角齿龙是一种濒危物种，仅分布在东北地区南部流入日本海的部分河流中。它的行为是未知的，因为它的人口密度在任何栖息地都极低。本研究在Hanzawa和Taniguchi（1982）曾调查过的福岛山形河水系和爱野河水系的Mogami河水系中村T. nakamurai和hakont .作为对照物种进行了生态调查。并利用活样本和死样本进行了取食实验和基于两种不同DNA标记的种群分析，明确了其行为和种群结构，并估计了其灭绝的紧急程度。虽然在无上河下游和甘野河上游均可采集到中村金蝇，但在无上河上游的个体数量较少。2006年和2007年，在河段已知产卵地均未见中村赤鳉个体，表明其产卵受到冬季异常温暖的抑制。对现存个体的观察表明，该物种是一种以鱼为食的动物，这表明这种食物习惯与其极低的种群密度有关。线粒体DNA分析表明，Mogami和Agano种群具有遗传分化，遗传多样性较低。同样，微卫星分析表明，所有种群的遗传多样性都非常低。这两项分析均首次在Mogami河下游发现了中村T.与hakont .的杂交品种。结果表明：1)中村赤潮种群的个体数量明显减少；2)赤潮种群的适合度可能因近亲繁殖和渐渗而下降；3)应将Mogami和Agano河种群划分为不同的保护单元；4)应立即保护赤潮种群的产卵地和栖息地。

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.