イカナゴ仔魚の日周鉛直移動と摂餌リズム〔英文〕

概要

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The diel vertical movement and feeding rhythm of the larvae of the Japanese sand-eel Ammodytes personatus were examined from the data of 7-8 series of MTD net tows taken through one day-night cycle on 3 cruises in February and March 1981 and March 1982.MTD net samples demonstrated a size-related diel change in the vertical distribution of sandeel larvae. Larvae less than 5mm in standard length (SL) didn't demonstrate diel vertical migration, but migration became evident in larvae 5-6mm in SL. They exhibited a pattern of vertical migration that was inverse to that commonly observed in other fish. Larvae were remarkably concentrated in 5- and 15-m tows during the day and were mainly caught in 30- and 50-m tows at night. Ascent and descent occurred at dawn and dusk, respectively. The range of diel migration increased with the size of the larvae. The diel changes in fullness of gut in both fieldcollected and reared larvae and the time to empty the gut in the laboratory indicated diurnal feeding activity. The advantage of this unusual pattern of migration is discussed from the point of view of feeding and predator avoidance.