Abstract
The patterns of geographic distribution and the geographic variations of some meristic characters in two types of Cottus nazawae collected throughout Hokkaido were investigated with special reference to the systematics of C.amblystomopsis obtained in Sakhalin.In Hokkaido, the small-egg type of C.nozawae is distributed along the Pacific and Okhotsk Sea slopes, while the large-egg type is distributed over most of Hokkaido.Towards the north, slight increases in number of vertebrae, pectoral fin rays and second dorsal fin rays were found in the large-egg type populations of Hokkaido, as well as a slight decrease in number of gillrakers.In the small-egg type populations, however, such “geocline”was not recognized except in the number of pectoral fin rays and gill-rakers.
Comparison of the external, particularly meristic, characters of C.amblystomopsis with those of the two types of C.nozawae suggests that the small-egg type should be identified as C.amblystomopsis.Accordingly, it is reasonable to apply the species name Cottus nozawae only to the large-egg type.
