The Japanese eel (Anguilla japonica; Japanese: 日本鰻 nihon’unagi) is a species of anguillid eel found in Japan, Korea, China, and Vietnam, as well as the northern Philippines. Like all the eels of the genus Anguilla and the family Anguillidae, it is catadromous, meaning it spawns in the sea, but lives parts of its life in fresh water. The spawning area of this species is in the North Equatorial Current in the western North Pacific to the west of the Mariana Islands. The larvae are called leptocephali and are carried westward by the North Equatorial Current and then northward by the Kuroshio Current to East Asia, where they live in rivers, lakes, and estuaries. The Japanese eel is an important food fish in East Asia, where it is raised in aquaculture ponds in most countries in the region. In Japan, where they are called unagi, they are an important part of the food culture, with many restaurants serving grilled eel, which is called kabayaki.
The Japanese freshwater eel produces a fluorescent protein, which makes it unique among vertebrates. This protein has been used in an experimental diagnostic test to assess liver function.