Abstract
Population density of five fish species was investigated at five valleys with different environmental characteristics. The investigation was carried out during non-irrigation period (January and February), irrigation period (May and June), and transitional period (August and September). As a result, it was found that distribution pattem of Numamutsu, Tamoroko, Simadojyo, Dojyo, Hotokedojyo were different By using analysis of quantification theory I, environmental factors for each fish were identified. The factors obtained were summarized as follows; 1) distance of ditch from Tanigashira (upper most of hill-bottom valley) to each station, and from Tanijiri (lower most of hill-bottom valley) to each station were extracted as environmental factor of Hotokedojyo; 2) From Tanijiri to each station, maximum depth, water velocity, rate of sand riverbed area in May and June for Simadojyo; 3) From Tanijiri and Tanigashira to each station, maximum depth, water velocity, rate of undercut bank area, rate of silt and sand riverbed area in January and February for Numamutsu; 4) rate of undercut bank area in January and February for Tamoroko; and 5) distance of ditch from Tanijiri and Tanigashira to each station, water velocity, rate of overhanging vegetation in August and September for Dojyo one year old or over.
