Anago Sushi
A Comprehensive Overview of Marine Eel in Japanese Sushi Cuisine

In the field of ichthyology, the Japanese term anago 穴子(アナゴ) generally refers to fish from the Congridae family, also known as conger eels. This family can be further subdivided into various subgroups: chin anago チンアナゴ, honmedama anago ホンメダマアナゴ and kuro anago クロアナゴ.

In a culinary context, particularly in the preparation of sushi, the genus conger, also known colloquially as anago, is of outstanding importance. This is mainly due to the appreciated texture and taste of its meat, which is often used in traditional dishes. Although species from other genera of the Congridae family are occasionally used for sushi, anago remains the preferred choice. A particularly prized species within this group is C. Myriaster, which is known as maanago マアナゴ in Japanese. This name can be translated as “real conger eel”, which underlines its esteem and its central role in Japanese cuisine. Maanago is characterized by its particularly tender meat and delicate aroma, which makes it a sought-after ingredient in high-quality sushi preparation.

Anago is counted among the traditional representatives of the cooked sushi ingredients (nimono dane). Therefore, prepared anago sushi is also often called ni anago 煮穴子. The broth that results from cooking the anago meat is boiled down, refined, and then used to glaze the meat. This tasty salty sweet sauce is called nitsume 煮詰め and is an essential part of the taste experience when eating anago nigiri sushi.

The meat is so soft that it almost falls apart and offers a full-bodied sweet taste. The texture is extremely pleasant and melts on the tongue. Anago harmonizes very well with vinegared sushi rice and is often preferred over freshwater eel (unagi) for the preparation of sushi. In contrast to unagi, anago is less greasy, sweeter and has a finer taste.

Nitsume or short tsume (つめ), is the golden brown colored sauce with which anago is glazed. It plays a central role in the process of preparation anago sushi and is decisive for the quality of the taste. Tsume is a thick sauce that is created by boiling down the broth from anago. The addition of the ingredients can vary and depends on the preferences of the cook. Most basic recipes consist of the anago broth left over from the preparation, some bones, and heads, alcohol, sugar, and soy sauce. The skillful balancing of the ingredients gives the tsume a sweet and spicy taste. Traditional or sophisticated restaurants often make them according to a personal, usually secret, recipe and prepare them from scratch each time. In inexpensive restaurants, industrially produced tsume is mainly used. When serving anago nigiri sushi, the sauce should not be poured or drizzled over the meat, but applied as a thin glaze with a brush.

The best season for anago is during summer. It is particularly tasty from July to August, when the fat content is at its highest and the taste is at its fullest. The rest of the year they are also very tasty, so that they can be enjoyed all year round.

Anago are predominantly nocturnal and start to search for prey at dusk. As carnivores, they feed mainly on small fish, crustaceans, mollusks, and small cephalopods. During the day, they hide in the sandy mud or in the crevices on the seabed. The species that live on the sandy, muddy bottom form groups and stretch their heads or even half of their bodies out of their burrows into the sea. The body shape of anago is elongated and cylindrical, the absence of scales is typical for the species. Adult specimens vary in length from about 30 cm to over 1 m, depending on the species. The distribution area ranges from tropical to temperate seas worldwide.

The family of the Congridae can be divided into three subfamilies:

The blood of the anago contains dinogunellin (ichthyotoxin), which is poisonous to humans and has a blood-dissolving effect. Even small doses can cause severe gastroenterological problems, nervous system disorders and pain. During preparation, care must be taken that the poison does not get into contact with mucous membranes, eyes or open wounds. The toxin is inactivated by sufficient heating above 70 °C or 158° F.^[1][2]

The toxin extracted from eel blood serum was used by Charles Richet in his Nobel Prize winning research, in which he discovered anaphylaxis.^[3]

Comparatively, few conger eels species are actively fished, but mostly end up as bycatch in the nets of industrial fisheries. A sustainable method is to catch them using special traps. These traps consist of tubes or hoses in which a potential prey is prepared. The traps are constructed in such a way that they taper off from the inlet. If a conger eel tries to get to the prey, it cannot leave the tube after passing the narrowing and can be collected by the fisherman. 

Japan consumes more than 70 percent of the world's eel catch, with about half coming from China, South Korea and Taiwan.