Unagi (うなぎ) is the Japanese word for freshwater eels, especially the Japanese eel, Anguilla japonica. Saltwater eels are known as anago in Japanese. Unagi are a common ingredient in Japanese cooking. Unagi is served as part of unadon (sometimes spelled unagidon, especially in menus in Japanese restaurants in Western countries), a donburi dish with sliced eel served on a bed of rice. A kind of sweet biscuit called unagi pie made with powdered unagi also exists. Unagi is high in protein, vitamin A, calcium, cholesterol and saturated fat.
Specialist unagi restaurants are common in Japan, and commonly have signs showing the word unagi with hiragana う (transliterated u), which is the first letter of the word unagi. Lake Hamana in Hamamatsu city, Shizuoka prefecture is famous throughout Japan as the home of the highest quality unagi; as a result, the lake is surrounded by many small restaurants specializing in various unagi dishes. Unagi is often eaten during the hot summers in Japan. There is even a special day for eating unagi, the midsummer day of the Ox (doyo no ushi no hi).
Unakyu, is the more common expression used for sushi containing eel.
Seafood Watch, a sustainable seafood advisory list, recommends that consumers avoid eating unagi due to significant pressures on worldwide freshwater eel populations. All three eel species used as unagi have seen their population sizes greatly reduced in the past half century. For example, catches of the European Eel have declined about 80% since the 1960s. Although about 90% of freshwater eel consumed in the U.S. are farm-raised they are not bred in captivity. Instead, young eels are collected from the wild and then raised in various enclosures. In addition to wild eel populations being reduced by this process, eels are often farmed in open net pens which allow parasites, waste products, and diseases to flow directly back into wild eel habitat, further threatening wild populations. Freshwater eels are carnivores and as such are fed other wild-caught fish, adding an additional element of unsustainability to current eel farming practices.