Unagi is the name given to freshwater eels indigenous to Japan, parts of China, and Korea. In Japanese, unagi is a generic word for freshwater eel of any origin, but has come to represent a specific kind of eel in the international culinary lexicon. The term is well known throughout the global cooking community as a specifically Japanese eel preparation. It is very common in sushi, in soups, or grilled and served over rice.
There are two main types of eel: those that live in freshwater and those that live in sea water. Freshwater eels indigenous to Japan are scientifically classed as Anguilla japonica. This type of eel lives in the shallow estuaries along the coasts Japan, Eastern China, and the Korean peninsula. The eels migrate into salt water to spawn, then return to rivers and streams to live out their lives. Compared to eels in other parts of the world, these are among the smallest.
Freshwater eel is considered a delicacy in Japanese cuisine in part because of how expensive the eels are. Eel farms exist in many parts of Japan, but their operation is costly. As carnivores, the eels need a substantial amount of protein each day in order to thrive. The demand usually requires regular harvesting from eels’ natural habitats, as well.
Most unagi is prepared with a grill. The meat is usually sliced very thin, then broiled or grilled on each side, cooking the meat through. A sweet marinade known as eel sauce is a common accompaniment to unagi. Precise eel sauce recipes vary, but usually include an eel stock, soy sauce, and sweet rice vinegar. This sauce is commonly added to an array of Japanese seafood dishes, including fish and shellfish preparations.
One of the most traditional ways of serving unagi is to simply lay the marinated, cooked strips over a bed of rice. Such a preparation is common in home cooking, in bento boxes — which are Japanese lunch boxes — as well as in restaurants. Noodle soup commonly includes the eel, and it is often served on its own.
Eel is rarely served raw in Japanese cooking. Even in sushi, eel meat is typically cooked, then either rolled into sushi maki mono, or served atop a small pad of rice nigiri style, often anchored with a thin belt of seaweed. Unagi sushi is one of the most common sushi dishes outside of Japan in large part because it is cooked. It is a first step for many sushi beginners.
The worldwide popularity of unagi sushi has led to some concern over the sustainability of harvesting the Japanese eel. Many conservationists fear that the rising demand will lead to over-harvesting, and will deplete indigenous populations. Habitat loss due to human development of the land surrounding many freshwater estuaries has also led to a general decline in eel population size.