Smelt, famous for ice fishing on frozen rivers and lakes during winter, is an anadromous fish that hatches in rivers, grows in the sea, and returns to rivers to spawn. However, those born in lakes may never enter the sea, spending their entire lives in the lake. In Japanese, it is called "wakazagi" and written as "公魚" in kanji. The character "公" is used because it was presented as a tribute to the Tokugawa shogunate during the Edo period.

In Japan, smelt, including shishamo and ayu, are classified as members of the Osmeridae (Cucumber Fish) family. These fish are named so because when fresh, they emit a scent resembling cucumbers or watermelons. Smelt are small, growing to only about 15 cm, making it easy to consume them whole, including the bones. They are typically prepared as tempura, nanban-zuke, or tsukudani (simmered dishes).