Abstract
Ayu (Plecoglossus altivelis) was an important indigenous freshwater fish in Taiwan. But it was extinct since 1968 due to habitat destruction and blockage of migratory routes. At 1984, ayu was transplanted into Peishi river and have reproduced successfully. We investigated the first 340bp of mitochondrial control region to reveal the relationship between ayu in Taiwan and Japan, and the population genetical structure of ayu in Taiwan.Fifty-seven samples were collected from Peishi, Tahan and Tachia river of Taiwan, 39 samples were collected from Hiki-gawa and Yoneshiro-gawa of Japan, and 3 samples were collected from Jiao river of Fu-chien, mainland China. The phylogenetic tree showed that the ayu populations of three rivers in Taiwan were composed both from Hiki-gawa and Yoneshiro-gawa. The result of population differentiation index (dA) and geneflow (Nm) indicate that the ayu population now in Peishi river were mainly from Hiki-gawa, the population in Tachia river were mainly from Yoneshiro-gawa and the population in Tahan river were mainly from Peishi river.The genetic diversity index (h andπ) shows that the haplotype diversity in each population is high, and the average haplotype diversity of Japan population is significantly higher than Taiwan population . Genetic drift and adaptive evolution maybe the main reasons responsible for the reduction in genetic variation of ayu population of Taiwan.