Unagi (鰻) on Doyō no Ushi no Hi (土用の丑の日)

Unagi served at Yoshinoya

Unagi ad at a convenience store

Unagi (Japanese eel) is considered a delicacy in Japan and is typically in season from October to December. Yet, it is most famously eaten during the summer — especially around Doyo no Ushi no Hi (土用の丑の日) which falls on July 19 and 31 this year. During this period, many advertisements can be seen at stores nationwide, and even restaurants that do not normally serve unagi often feature it on their menus.

So, what exactly is Doyo no Ushi no Hi? Doyo (土用) refers to an 18-day period before the start of each season, based on the traditional Japanese calendar. Ushi no Hi (丑の日) means "Day of the Ox," one of the 12 animals in the Chinese zodiac. While the zodiac is often used to mark years, it was also used to mark days as well. Therefore, Doyo no Ushi no Hi simply means "Ox Day during the Doyo period." Although there are four Doyo periods each year, the one before autumn — typically in late July to early August — is the most widely recognized.

Unagi served at Kura Sushi

If unagi is in season in the fall, why eat it now? The tradition stems from a custom of eating foods that begin with the "u" sound — like ume (pickled plums), udon (noodles), or uri (melon) — on Ox Day, as these were thought to promote health and stamina during the hot summer and bring good luck. The association of unagi with this day is thought to stem from a catchphrase created by Hiraga Gennai (1729–1780), an Edo-period (1603–1868) scholar, who coined the phrase "Unagi on Doyo Ushi no Hi" to help a struggling unagi restaurant owner increase sales during this period.