Katsuo (Bonito) Sushi

Katsuo (Skipjack tuna / Bonito)

Red Fish

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Order Perciformes, Family Scombridae, Tribe Thunnini, Genus Katsuwonus

A large carnivorous migratory fish that inhabits warm seas around the world. In Japan it lives mainly on the Pacific side and is rarely seen on the Sea of Japan side. Large ones reach 1 m in length and 20 kg in weight, but most of those caught are around 40 cm.

Bonito is a large carnivorous migratory fish that inhabits warm seas around the world, preying on small fish and crustaceans. Its Japanese name is said to come from "katauo" (hard fish), because dried bonito is hard, which was later shortened to "katsuo." In Japan, bonito is mostly found on the Pacific side. Each spring it rides the Kuroshio Current flowing from south to north around Kagoshima and heads north, and in autumn, when it meets the Oyashio Current off Miyagi Prefecture, it makes a U-turn and heads south, repeating this cycle. Like tuna, it cannot take in oxygen by moving its gill covers as other fish do, so it takes in oxygen by swimming, and dies if it stops. Bonito has two seasons, spring and autumn. The "hatsugatsuo" (first bonito) heading north from around Kagoshima in spring is lean with a light, refreshing flavor, while the "modorigatsuo" (returning bonito) heading south off the Sanriku coast in autumn has eaten plenty of food, so it is fatty and rich. Today the fattier kind is more popular, but in the Edo period, when first-of-the-season foods were prized, the first bonito was so popular and expensive that people said, "Eat it even if you have to pawn your wife." Bonito is also rich in nutrition, containing high-quality protein and plenty of iron, as well as DHA and EPA that help prevent heart disease, and niacin that is good for the skin. Being delicious and highly nutritious, it is naturally a popular sushi topping, served everywhere from high-end sushi to conveyor-belt sushi, though because it spoils easily it is sometimes considered a difficult topping for sushi restaurants to handle.

Various Ways to Enjoy Bonito Sushi

The species used as a sushi topping is mainly the one called hongatsuo (or simply katsuo), and the condiment used is often ginger rather than wasabi. There are many variations of bonito sushi, enjoyed in a wide range of ways: served raw, seared, prepared as tataki, or marinated as zuke. In Mie Prefecture, one of the top areas for bonito catches, "katsuo no tekone-zushi"—lean bonito marinated in soy sauce and mixed with vinegared rice, then garnished with shiso leaves, ginger, and nori—is also beloved as a local dish.

Tekone-zushi, a local dish of Mie Prefecture made with bonito

The Mystery of the Bonito's Stripes

Many people picture bonito with stripes on its belly, but in fact bonito normally has no stripes.
Stripes appear when it is excited: horizontal stripes appear when chasing a female, and vertical stripes appear when it is about to die. Note that "vertical stripes" are those that run vertically when the fish's mouth is held upward, so what we usually see is not horizontal stripes but vertical stripes. Some believe the stripes appear to make the fish stand out or to startle enemies as a form of countershading (a kind of camouflage), but this is not clearly understood. Living creatures really are mysterious, aren't they?