イカナゴ卵の浮游性と瀬戸内海における分布

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Though the eggs of sand-eels (Ammodytes personatus GIRARD) have been established as demersal and adhesive ones since INOUEs experiment (1949), the present author have collected them by horizontal haul with a larval net even at sea surface. The eggs are spherical in shape, measuring 0.85-0.95mm in diameter, with a single yellow oil globule. The egg membrane is transparent but usually sticked by minute particles of foreign materials, and the perivitelline space is wide. The newly hatched larva is 4.3mm in total length, with the oil globule in the posterior part of yolk, and with filamentous organs along on each lateral side. (Fig. 1 a-e.) The eggs occurred most abundantly during the period from the end of December to the middle of January, and distributed mainly in areas of rapid tidal current such as the central part of Bisan Seto. As for vertically, the eggs were supposed to distribute more abundantly in the deeper layer. (Fig. 2, Table 1) Those eggs which are adhesive in the laboratory do not always exhibit the same nature in the sea, and there is a possibility that sand-eel eggs may be demersal but non-adhesive in natural circumstances. Under certain circumstances such as shallow water, rapid tidal cur-rent and topographical up-welling, sand-eel eggs are whirled up and distribute even in the surface layer.
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