Japanese capelin, shishamo smelt. ししゃも, 柳葉魚。Spirinchus lanceolatus.
A fish originally caught in autumn in the mouths of the rivers in Hokkaido (it swims from the sea into the river mouths to lay its eggs). A slim fish, about 15 cm long, with a silver underside and darker backside. Usually dried and eaten grilled. At its tastiest when carrying roe (ko-mochi shishamo).
The characters with which the name traditionally is written literally mean "willow leaf fish," and that tallies with the meaning of the name which is originally from the Ainu language.
As the number of shishamo in Hokkaido has decreased, one today usually finds imported capelins from the northern Pacific on the Japanese dining table. The real shishamo now is a rare delicacy.