然別湖産イワナの変異性に関する研究

III.オショロコマSalvelinus malmaの地理的変異と然別湖産イワナの形態的特徴

抄録

Geographical variations of some meristic characters of the Dolly Varden, Salvelinus malma, which were collected in some districts (Nome, Anchorage, Juneau and Seattle) of North America, Bering Sea, Okhotsk Sea and in some rivers of Hokkaido, were investigated with special reference to the systematics of the Miyabe char, S.malma miyabei, in Lake Shikaribetsu in Hokkaido.An obvious “geocline” associated with an increase in the number of vertebrae, gill-rakers, dorsal rays and pored scales of the north American populations was found.Toward the east and toward the uplands, slight increases in the number of vertebrae and pored scale were observed in the land-locked populations of Hokkaido. No significant differences were recognized in the number of anal rays among populations of the Dolly Varden, however, pyloric caeca were slightly fewer in Hokkaido populations than in the others.Meristic characters of the Miyabe char, excepting gill-rakers, were similar to those of Dolly Varden living in Hokkaido.A striking characteristic of the Miyabe char was found in the number of gill-rakers, as well as accessory gill-rakers in the medial surface of the gill arch.Gill-rakers of the Miyabe char were the most numerous among all Dolly Varden investigated.It was discussed that, in relationship to food habitats of the anadromous Dolly Varden, the changes in morphology might be an adaptation to plankton feeding.