It is important to make clear seasonal changes of fish habitat quality in rivers. There are still many unsolved question in fish habitat quality, because this consists of quite complex system. In this study, field surveys of seasonal changes of fish habitat quality were conducted through nine months in Itabitsugawa river which belongs to class B river. It was found that Carassius langsdorfi moves from pool to riffle through winter to summer. Zacco temminckii and Zacco platypus evade Carassius langsdorfi in all seasons, because the body length of Carassius langsdorfi is larger than that of Zacco temminckii and Zacco platypus. Further, Zacco temminckii evades Zacco platypus which is larger than 8cm of body length.
