ヒイラギの卵発生と仔魚前期
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概要
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Leiognathus nuchalis (TEMMINCK et SCHLEGEL) is a common leiognathid fish of Japan, mainly distributed along the coasts of south-western part of the territory as well as in Korea and China. It appears to inhabit the shallow coastal regions. The spawning season seems to extend from the middle of May to the end of July in northern Kyushu. On June 22, 1959, the author carried out the artificial insemination of this fish at Moji City, Kyushu, and observed the egg development and hatched larvae. The egg is bouyant and colorless, spherical in shape measuring 0.6-0.65mm in diameter, with a single oil-globule measuring 0.12-0.15mm. The yolk and egg-membrane have no particular structure. Hatching took place in 30 hours and 45 minutes at the water temperature 22.5-23.9°C. In the course of development, melanophores and xanthophores appeared on the embryonal body and surface of oil-globule in 2-3 hours before hatching (Figs. 1-9). Newly hatched larva (Fig. 10), measuring 1.4mm in total length, had 8-9+17=25-26 myotomes (the number of vertebrae of this fish is 10+14=24). The hatched larvae were floating in the water near the surface with the yolk upwards. The melanophores were seen on the back side from head to tail and on the surface of oil-globule. The xanthophores were distributed on the head, trunk, middle part of the tail forming cross bands, and on the surface of oil-globule and yolk surface around the oil-globule. Five or six hours old larvae (including the one of Fig. 11) were 1.63-1.95mm in total length. The groups of xanthophores appeared on the head, back of the front part of trunk, back and abdominal side behind the anus and middle of the tail. 39 hours old larva was 2.1mm in total length. The yolk was not yet wholly absorbed. The eyes were becoming black. They were floating vertically in the water with the head downwards. The larvae, 65 hours after hatching (Fig. 13), nearly consumed the yolk and reached 2.15-2.20mm in total length, with the anus being slightly shifted forwards. The number of myotomes was 6+19=25. The larvae swam freely in the water.
- 公益社団法人 日本水産学会の論文