キビナゴ(<i>Spratelloides japonicus</i> (H<sub>OUTTUYN</sub>))の生活史に就いて

Abstract

The species is a clupeoid fish distributed from the seas of Indo-Australian Archipelago to Central Japan. Its egg having rather thick egg membrane (Fig. 1) measures ca. 1mm. in dia The spawned eggs stick to each other making cluster and adhere to the substratum in the sea, so they are not pelagic but adhesive and demersal. The yolk is translucent with some yellow tinge and has the reticulate structure characteristic to the eggs of clupeoid fishes. Artificial fertilization is rather easy. Eggs artificially fertilized hatch by 6 to 7 days at 21-23°C. Newly hatched larva has elongated form, its anus situated far backward as in the case of other clupeoids. The dorsal fin shifts anteriorly during development over a distance of about 16 to 18 myotomes, but the anus and the ventral fin scarcely change their initial situations (the anus lies at 35th or 36th myotome; the ventralfin at 20th or 21th myotome). During the development of the embryo some special blastomeres make appearance at the margin of blastoderm at early stage and later they lie rather in extra-embryonic region, so the blastoderm disc shows irregular form unlike other teleostean eggs (Fig. 2, 3). Those blastomeres persist from an early stage of the embryo until hatching or later. In some of the said blastomeres get out of the embryo and lie freely in the perivitelline space. The post-larva of the present species can be distinguished from those of other clupeoid fishes of Japan, i.e., Sardinia melanosticta (TFMMINCK & SCHLEGEL) and Etrumeus microps (TEMMINCK & SCMLEGEL, ) by the presence of the characteristic black pigments arranged along the borders between myotomes (Fig. 10-16). The silvery lateral band along the side of the body begins to appear at the stage of ca. 30mm. of the body length. (See Fig. 1-19).