A cluster analysis of freshwater fish fauna of 30 rivers on 13 islands in the Seto Inland Sea and 17 short rivers on the mainland of Hiroshima Prefecture revealed two island groups, based on fish species composition: eastern islands group (8 islands) and western islands group (5 islands). The fish fauna of the western islands group showed a greater resemblance to that of the mainland rivers than shown by the eastern islands group, indicating differing geographical relationships between the island groups and between the latter and the mainland.
