Abstract
Environmental structures and fish fauna were compared between reaches of a spring-fed small stream, Yagawa Stream which has been used for agricultural irregation, a branch of the Kinu River in Tochigi Prefecture. Seven factors were selected for the analysis of emvironmental structures : i.e., 1) riparian plant, 2) driftwood, 3) undercut bank, 4) overhanging vegetation, 5) connected ditch, 6) submerged plant, and 7) gravel riverbed. Measurement of the factors and fish sampling were carried out at 11 sampling sections in each season of 1996 and 1997, and stream types were classified by cluster analysis on the environmental factors. Then the species composition of fishes was compared in relation to each emvironmental factor and the stream types.
As a result of the cluster analysis of the environmental factors, Yagawa Stream was devided into three parts, the slope-side section, the paddy field section and the transitional section. The nektonic fishes inhabited mainly in the slope side section and preferred to driftwood, while the benthonic fishes inhabited mainly in the paddy field section and were closely related with riparian plants, submerged plants and connected ditches. These results agreed well with facts that spawning redds of Oncorhynchus masou masou were found in the slope side section and the transitional section, and that those of Lampetra reissneri were in the paddy field section.
