Abstract
Seasonal changes in the loach population in different aquatic habitats surrounding paddy fields in Ehime Prefecture were investigated so as to establish the parameters necessary for stable propagation. Habitats were classified into three types: paddy fields, temporary creeks and permanent creeks. Adult or sub-adult loaches, which overwintered in the permanent creeks, entered paddy fields via temporary creeks at the beginning of the irrigation season. In the paddy fields, they spawned and reproduced until midseason drainage of the former. An increase in the number of juvenile loaches in the temporary creeks just before midseason drainage, indicated their having begun to disperse. During midseason drainage, the loaches moved primarily towards temporary and permanent creeks, seldom returning to the paddy fields. A survey of these habitats in autumn suggested that the species overwinters mainly in permanent creeks, the life cycle of loaches residing in habitats surrounding paddy fields, therefore being regulated by water-level control for agricultural purposes. The three habitats served different functions during the life cycle of the loaches, paddy fields being sites for reproduction, permanent creeks for overwintering and temporary creeks for dispersal.
