西部北太平洋のウナギレプトケファルスの日令と産卵期〔英文〕

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In order to determine the spawning season of the Japanese eel Anguilla japonica, age and birth date of the leptocephali were estimated with the daily growth increment in otoliths of 14 specimens collected in Western North Pacific in September 1986.The sagittae of the leptocephali (40.5-47.0mm in TL) were translucent, laterally compressed oval structures of about 155μm diameter with a dark opaque core (6μm in long axis) in the center. Distinct concentric growth increments (ring) were observed around the core from the center till the edge of otolith. About 80% specimens examined had a distinct dark ring (heavy discontinuous zone) with about 11μm diameter near the core, which seemed to be a "hatch check" formed at hatching.The age of leptocephali was nearly uniform, 72±3 days (mean±SD). Their birth date ranged from June 28 to July 18, 1986 and the mean was July 13, suggesting that this species spawns in summer.
日本水産學會の論文