ワカサギ（Ｈｙｐｏｍｅｓｕｓ ｔｒａｎｓｐａｃｉｆｉｃｕｓ ｎｉｐｐｏｎｅｎｓｉｓ）の口部・歯系の性差

Abstract

The form of bone and the distribution of teeth in the mouth have been used to indicate interrelationship of genera in the Osmeridae. But sexual differences in the form of bone and dentition in the mouth in adult smelt, Hypomesus transpacificus nipponensis, have not been clarified yet. This paper reports on the sexual difference of sizes of head and conical teeth and of numbers off unctional teeth, tooth germs and traces of lost teeth in the mouth between the two sexs in adult smelt collected from the Lake Abashiri on January 27, 1982.The lengths of head, dentary and conical teeth on the pre-maxillary in males were significantly larger than those in females. The total number of teeth (functional teeth and tooth germs) and tooth germ number in males were significantly larger than those in females, but the number of trace of lost teeth on dentary in females was larger than those in males. Also, the rate of ocurrences of smelt with traces of lost teeth on dentary in females were significantly higher than those in males. On the other hand, the rate of occurrences of toothgerms in the tooth rows on dentary and pre -maxillary of 90-95mm SL (standard length) were significantly higher than those of 70-75mm. And, the rate of occurrences of toothgerms in the tooth rows on the two bones of 103-125mm SL in 1+year-old fish were higher than those of 65-90mm SL in 0+year-old. These results may associate with the life history of adult smelt during the spawning period.