The chum salmon populations collected from 21 rivers in Japan were analyzed by using as markers the three genes, Idh-A2, Idh-B2, and Ldh-Al, controlling IDH and LDH isozymes.
(1) No differences in gene frequencies at the three loci were found between the sexes or between the years of catch.
(2) Any two of the 21 river populations showed clear differences of gene frequencies, indicating that they are independent of each other.
(3) The chum salmon populations in Japan could be divided into at least 3 groups: Hokkaido group, and the Pacific Ocean and Japan Sea groups of Honshu.
(4) A geographical cline of gene frequencies was observed in each of the Pacific Ocean and Japan Sea groups of Honshu, the phenomenon suggests that there has been a mixing of chum salmon individuals between neighboring rivers, though on a small scale.