Abstract
Spawning ecology and seasonal migration of Tanakia lanceolata were investigated in the irrigating area of the Iwaki River Basin in northern Japan. Two unionid mussel species, Inversiunio jokohamensis and Pronodularia japanensis, were mainly used by T. lanceolata as the spawning hosts in this study area. The results of body length composition and mark-recapture experiment suggested that there were seasonal and ontogenetic habitat change. In spring, a large number of adult and immature of T. lanceolata, gathered to their spawning ground in branch ditch, and alternative pattern was dispersal from branch ditches in autumn. Limitation of the distributional area of the host mussels and seasonal change of the physical environments could affect their migration patterns. Because the branch ditch was also comfortable for larvae and juveniles of T. lanceolata as nursery grounds, channel networks should be ensured for fish conservation.
