Abstract
The Yagawa stream, a primarily canal-fed agricultural waterway in the west Kinugawa district, Tochigi Prefecture, Japan, and an upstream, spring-derived waterway were surveyed from October 2002 to May 2005, using trapping and marking and recapture methods, to establish the migration characteristics of Hotoke-dojo loach between the upper and lower portions of the waterway system. The ecology of the loach was also studied, considering the relationships between migration and seasonal changes in environmental factors and maturation of individuals. Although the Yagawa stream flowed throughout the year, the spring and associated waterway dried up for about two months and one month, respectively, every winter. Trapping resulted in the capture of many individuals each spring (from late March to early June), the number having increased progressively over autumn and winter (October to February). Upstream migration in the Yagawa stream to the spring-fed waterway began immediately after water started to flow in the latter in spring, mature individuals comprising 64.7% of the migrating individuals in 2004 and 70.7% in 2005. The numbers of migrating loach in autumn and winter was positively correlated with differences in water temperature between the Yagawa stream and the spring-fed waterway. Marking and recapture confirmed that individuals migrated from the latter downstream to the Yagawa stream during this period. The results indicated that Hotoke-dojo living in the survey area spawned in the spring-fed waterway, a temporary aquatic area, and overwintered in the constantly flowing Yagawa stream.
