Oplegnathus fasciatus (Temminck et Schlegel) is a coastal fish, attaining some 60 cm. in total length, found on the rocky coasts of the whole extent of Japan. According to the catch records of the floating eggs the spawning season, in Kyushu, seems to extend from May to July. It seems to me from the time records of catches that the spawning happens within several hours after or before sunset (Table 1). On May 29, 1954, at Tamanoura Cho (Goto Islands), Nagasaki Prefecture, Kyushu, the author operated artificial insemination of this fish and observed the development of the eggs and hatched larvae (Plate 15, figs. 1-12). The egg is colorless and bouyant, spherical in shape, measuring 0.86-0.95mm in diameter. The yolk is roughly segmented near its animal pole, with a single colorless oil-globule measuring 0.16-0.23 mm in diameter. Hatching took place in 1 1/2 days at the water temperature 20.6-23.4℃, when the embryo encircles 3/4 of the yolk surface (Fig. 9). The larva just hatched is 2.1-2.3 mm in total length, with the oil-globule lying in the anterior part of the yolk which does not protrude beyond nozzle. The myotome number is 11+16=27 (vertebral number of this fish is 10+15=25). In four days after hatching the yolk was entirely consumed and the jaws of the mouth formed.