Early life history characteristics and genetic homogeneity of Conger myriaster leptocephali along the east coast of central Japan

To study the population structure of the Japanese conger eel, Conger myriaster, we investigated the age, total length, developmental stage and mitochondrial (mt) DNA genetic variation among the leptocephali collected from three different locations along the east coast of central Japan. A total of 79 individuals was collected at the same period of time in March 1998 from Iwaki (northern site), Odawa Bay (middle site) and Ise Bay (southern site). Results from morphological measurements and otolith age determination indicated that the mean total length of leptocephali from Iwaki was about 10 mm shorter than those from Odawa Bay and Ise Bay, the average age of the samples from Ise Bay was about 50 days older than those of the sample from Iwaki and Odawa Bay, and the leptocephali in metamorphic stage appeared only in Ise Bay samples. The otolith data also suggested the existence of at least two spawning seasons in 1997. These regional differences suggested that the early life history characteristics of the Japanese conger eel might differ between geographically different areas along the east coast of central Japan. Phylogenetic analysis based on mtDNA sequence data indicated no significant genetic differentiation between samples collected from different locations, implying intensive gene flow between geographically distant areas.