アジメドジョウの生息地保全に関する生態学的研究

概要

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The Ajime loach, Niwaella delicata, is endangered and categorized as a vulnerable species in the latest Red List of Threatened Animals in Japan （2007）. In the present study, field investigations and aquarium-based experiments were conducted to reveal the suitable habitat for this fish. The outcome of field investigations indicated that major variables influencing distribution of the fish are low summer water temperatures, variable channel units, an abundance of loose stones and abundant groundwater discharge and also that, in autumn, the hiding of the fish under substrates is followed bymigration to groundwater seepages in order to overwinter. Meanwhile, aquarium-based experiments showed that the Ajimeloach prefer a large substrate about 40 cm in diameter, and multi-layered loose stones for the hiding. Furthermore, the fish proved to have positive rheotaxis and thermotaxis, indicated by sensitivity to differences in water flow of 0.5 cms^<-1> and water temperature of 1.3 ℃ ± 0.1 SD, respectively. The rheotaxis and thermotaxis of the fish probably play an important role in the finding of groundwater seepage. In the last chapter of this paper, based on the results of these investigations and experiments, I discuss the river management needed to conserve the suitable habitat for the Ajime-loach.