メイタガレイの卵発生と仔魚前期

Abstract

Pleuronichthys cornutus (TEMMINCK et SCHLEGEL), the small turbot, is commonly distributed along the coast of Southern Japan and caught with much commercial importance. On December 6, 1963, the authors carried out the artificial insemination of this fish at Shimabara City, Kyushu, and observed the egg development and hatched larvae. The spawning season seems to extend from the middle of November to the end of December in Ariake Sound which the City faces. The egg is bouyant, colorless and spherical in shape, measuring 1.03-1.11mm in diameter. The egg has many small oil globules in early developmental stages, but the globules unite in from one to some large ones in gastrula stage. The egg-membrane has a hexagonal pattern of approximately equal size, measuring about 0.018mm across. The hatching took place in 115 hours at the water-temperature about 14.0°C. In the course of development, the embryonal body bears thickly melanophores and xanthophores. The newly hatched larva, measuring about 2.80mm in total length, had 12 ?? 13+24=36 ?? 37 myomeres (the vertebra-number 36-38). The anus opens at about the mid point of the body. The almost whole body is scattered with melanophores and xanthophores except the posterior part of the tail, where these chromatophores appear along the dorsal and ventral margins. The chromatophores appear thinly on the yolk sac. The 13 hours old larva is 3.69mm in total length, and its eyes are becoming black. The mouth opened at about 35 hours after the hatching. By 60 hours after the hatching the yolk was almost absorbed and the pectral fins appeared. The chromatophores of the head and the mid part of the body expand to the dorsal and ventral fin folds. Comparing this larva with the ones of Californian turbots of the same genus the following similar characters were found. 1) The anus opens almost mid part of the body.2) The chromatophores of the body are very thick, not forming cross band, and some ones expand to the fin fold.