Population structure and recruitment mechanism of Muraenesox cinereus leptocephali using otolith microsturucture and mitochondrial DNA sequences

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The growth history and recruitment of Muraenesox cinereus were studied, based on growth increments in sagittal otoliths of leptocephali collected from Nobeoka (Miyazaki Pref.), Yatsushiro (Kumamoto Pref.), Onomichi (Hlroshima Pref.), Kamakura (Kanagawa Pref.) and off Goto Islands (East China Sea) in 1999 and in 2000. The periodicity of increment formation was confirmed by treating leptocephali with alizarin complexon and examining otoliths after a known time period. The formation rhythm of otolith increment was about 0.13/day in leptocephalus stage, 0.5/day in metamorphic stage and 1/day in juvenile stage, respectively. Examination of otoliths showed that leptocephali recruiting to Nobeoka Bay devided into two age groups, 150-200 and 250-300 days old. Back calculated hatching dates were distributed throughout most of the year, with a peak in summer and winter.Mitochondrial DNA sequences that include a part of the cytochrome b gene to the first half of the control region of Muraenesox cinereus leptocephali were determined to evaluate the population structure of the species. A total of 591 nucleotide site, including cytochrome b gene to the first half of the control region, was sequenced from specimens from Nobeoka, Yatsushiro, Kamakura and East China Sea. Out of 396 nucleotide sites on the control region, 31 (7.8%) variable, 16 haplotypes being found. Differences between nucleotide sequences ranged between 0.25 and 4.55% with average of 1.88%, indicating that the control region of the mitochondrial DNA in the species is characterized be high variability. The phylogenetic tree constructed by the neighbor-joining method shows neither significant geographic clusters. This result indicate that the present specimen might come from a single population.