Abstract
Anguilla marmorata Quoy & Gaimard 1924 is widespread in the fresh waters of the islands and the coast of the Indo-Pacific Ocean. It was found that there are two major upstream migrations of the eel and reaches a peak during the summer time. The otolith data also indicate that there are two major spawning seasons in a year (summer and winter). For the constant recruitment patterns, we would like to know whether the separation of spawning seasons results in the differentiation of A. marmorata populations. In this study, 128 migratory elvers were collected from November 1995 to May 2001 at Hsiukuluan River in Eastern coast of Taiwan. To reveal the genetic population structure, neighbor-joining tree and multidimensional scaling (MDS) analysis were done from the first 566 bp of the mitochondrial control region, and the coefficient of nucleotide differentiation (Nst) and gene flow (Nm) were estimated. No significant difference were found between different recruitment populations, indicated that the separation of spawning seasons did not lead to the division of A. marmorata populations. However, results of both neighbor-joining tree and MDS analysis indicated that A. marmorata in the North Pacific Ocean may not be a panmictic population. Considering both current and genetic data, we believe that there may be several subpopulations of A. marmorata in the North Pacific region, and furthermore, each subpopulation has its own spawning area.