Long term changes of population genetic structure of the Anguilla Japonica in north Taiwan

The Japanese eel Anguilla japonica, is a catadromous fish widely distributed in northeastern Asia, south from Taiwan, through mainland China, Korea and north to Japan. The spawning ground of the eel is located in the west of Mariana Islands (13-15°N, 142-143°E). The leaf-like larvae leptocephali are drifted westward with North Equatorial Current and then turn northward with Kuroshio Current near Philippines. At arriving continental shelf, they metamorphose to glass eels, and become pigmented elvers in the estuaries. The elvers spend 4-10 years growing through yellow eel stage and silver eel stage, after that time they go seawater spawning migration, lay eggs in the deep sea and die.

Anguilla japonina is an important economical fish in Taiwan, its resource however fell down after 1970s. Tseng et al. (2003) used polymorphic microsatellite loci in the genomic DNA to examine the variation of population genetic structure of the eel in north Taiwan during 1997-1999. The results showed no genetic differentiation among 1997-1999, but the mean observed heterozygosity (Ho) declined among those years. In the present study we use 6 polymorphic microsatellite loci to analyze long term population genetic structure of Japanese eel among 1986-2007. We test first：If the eel resource declined, would their genetic structure and variation be affected? Second：What is the correlations among year cohorts? Do their genetic structures follow their life cycle? Third：Dose the mean observed heterozygosity (Ho) decline in the latest twenty years?

In this study we used a total of 1150 Anguilla japonica elvers for analysis of population genetic structure. The results showed very low genetic differentiation indices among years but with significant difference (Fst=0.004, p<0.001). In phylogenetic tree result, all bootstrap values were low, meaning low population differentiation among samples. The isolation by time (IBT) test showed no significance (p=0.249). The mean observed heterozygosity (Ho) and total number of alleles do not dramatically decline in the latest twenty years. In conclusion, the population genetic structure of the Japanese eel has no significant changes in the latest twenty years, and its genetic diversity keeps stable.