Unagi

Two regional methods developed. In the Kantō region, eel is split along the back, grilled plain, then steamed to make it soft and remove fat, and finally grilled again with tare. In the Kansai and further west, eel is split along the belly and grilled directly without steaming, which gives a crisper surface and firmer flesh. A popular explanation is that the samurai of Edo avoided the belly cut because it recalled ritual suicide, though this is folklore rather than history.

Other preparations include shirayaki, grilled without sauce and eaten with wasabi and soy sauce, and umaki, eel rolled in omelette.

Eel is almost always eaten with rice. The serving vessel gives the dish its name, and eel restaurants usually offer several grades that differ in the amount of eel.

The Day of the Ox in the summer doyō (doyō no ushi no hi), which falls in late July or early August according to the traditional calendar, is the day on which eel is traditionally eaten to gain strength for the hot season. Popular tradition credits the Edo-period scholar Hiraga Gennai with inventing the custom to help an eel shop sell in summer, but there is no firm evidence for the story.

Eel is in fact fattest in autumn and winter, but the summer custom remains strong, and supermarkets and convenience stores take orders for eel weeks in advance.

Almost all eel eaten in Japan is farmed, but eel farming depends on glass eels caught in the wild, since breeding eels commercially from eggs has not yet become economical. Catches of glass eels have fallen sharply since the mid-twentieth century. The Japanese eel was listed as Endangered on the IUCN Red List in 2014, and the European eel, formerly imported in large quantities, is critically endangered and its export from the EU is banned.

Japan, China, South Korea and Taiwan have agreed to limit the amount of glass eels put into farms, and research institutes are working on full-cycle aquaculture. The debate over whether eel should remain a mass-market food is ongoing.