Allozymic Variation and Regional Differentiation in Wild Populations of the Fish Oryzias latipes

Abstract

Allozymic variation was studied at 21 loci in Japanese wild populations of the freshwater fish Oryzias latipes, collected at 53 localities. By means of the unique alleles at the Adh, Pgm, Idh and Sod loci, the Japanese populations could be divided into two major groups, the 'Northern Population' and the 'Southern Population.' No clinal distribution was observed at these loci, but the boundary of two regions was very distinct. The Southern Population was further divided into five subpopulations by the unique alleles at Acp, Amy, Aat, Me and Pgd. In this case also, the boundary was clear. The Northern Population was very homogeneous. On the other hand, the Southern Population was variable. These results show that Japanese wild populations of medaka are remarkably differentiated regionally. As little clinal distribution is observed, it is supposed that the differentiation is primarily due to geographical isolation.