Freshwater fish faunas of 44 rivers (504 sites) flowing into the Seto In-land Sea in Hiroshima Prefecture, western Honshu, Japan, were analysed with se-lected environmental factors of rivers. The cluster analysis of fish fauna revealed that these rivers were divided into three groups: long-length, middle-length, and short-length of rivers. There was significant correlation between the river length and the total number of fish species. Such a pattern was clearer in the genuine freshwater fishes rather than in the diadromous fishes.
