Abstract
Young of giant sciaenid, Argyrosomus japonicus (Temminck et Schlegel), were collected from coastal water of Kochi Prefecture, Japan. The young specimens, 18.0 to 44.9cm in total length, were compared morphologically and electrophoretically with adults, 72.5 to 135.0cm.
Some morphological characters of the young did not agree with those of the adult described by a few researchers. It was ascertained that the proportions of head, orbit, and fin ray length changed gradually in relation with growth. Internal morphological characters, such as sagitta, diverticulum of the air-bladder, interorbital septum of neurocranium, show also changes in their shape. The form of caudal fin, which was one of the most important diagnostic characters of this species, also changed continuously from cuneate to truncate. These morphological changes seemed to be the reason why the young had never been recorded until now. There is a possibility that Nibea mi-ichthioides (Chu, Lo et Wu, 1963) which was synonymized with Argyrosomus amoyensis (Bleeker) by Trewavas (1977), may be the young of this species.
To examine genetic identity of the young and adult specimens, the isozymes of muscle and liver were separated by starch-gel electrophoretic method. All of the alleles examined in the young well accorded with those of the adult.
