The Japanese word for freshwater eel, a common sushi topping, is unagi.
Unagi usually refers to freshwater eels, especially the Japanese eel, rather than to a particular sushi shape. In sushi restaurants it is commonly served as a cooked, glazed slice over rice. The preparation is often associated with kabayaki: the eel is filleted, skewered, grilled, and basted with a sweet-savory tare sauce.
Unlike many fish served as sushi, unagi is not eaten raw. Freshwater eel blood contains a toxin that is neutralized by cooking, so commercial unagi is typically sold and served cooked. It also appears in dishes such as unadon, eel over rice in a bowl, and unaju, eel over rice in a lacquered box.
A frequent mix-up is anago, which means conger eel and refers to a saltwater eel. Saba is mackerel, while hamachi is usually yellowtail. Unagi sushi may also be paired with cucumber in a combination called unakyu. Because wild eel populations have declined, farmed or substitute eel species are increasingly used in some markets.