Abstract
The larvae of the Japanese eel, which were hatched from fertilized eggs obtained from silver eels matured artificially by hormone treatment and kept in sea water at 23°C, were observed.
1) The newly hatched larvae measured about 2.9mm in body length and had about 40 somites, Their mouths and anuses were still unopened. Their membranous fins developed well, but their other fins could not be found. Very few pigments were recognizable only in the caudal portion of the embryo.
2) The larvae survived for about five days. They respectively measured about 4.8mm, 5.3mm, 5.9mm and 6.2mm in body length on the second, third, fourth and fifth days respectively after hatching. By the sixth day, when the yolk sacs of the larvae were almost absorbed, most larvae showed a curvature of their tails. The average length of the surviving larvae was about 5.8mm.
3) By the third day after hatching, mouths and anuses opened and pectoral fins appeared. The brain differentiated into three parts, showing a large fourth ventricle. The larvae, on the sixth day, showed conspicuously developed jaws with clear tooth anlagen. Fifty-three preanal and about 48 postanal myomeres were counted in the larvae.
