is a saltwater fish about 15 centimeters in length. It is slim and resembles a willow

Willow

Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

 leaf; the Japanese

Japanese language

is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

 name, shishamo, is derived from the Ainu

Ainu language

Ainu is one of the Ainu languages, spoken by members of the Ainu ethnic group on the northern Japanese island of Hokkaidō....

 name for the same fish, susam, which is supposed to be derived from a compound of Ainu susu "willow" + ham "leaf", hence its name in kanji

Kanji

Kanji are the adopted logographic Chinese characters hanzi that are used in the modern Japanese writing system along with hiragana , katakana , Indo Arabic numerals, and the occasional use of the Latin alphabet...

 (jukujikun, where the characters have no phonetic relation to the word). It is generally dark on the back with a silver-white underside. The Shishamo is a Japanese delicacy and is grilled or fried whole and served with its roe intact (ko-mochi-shishamo).