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Maguro (Tuna) Sushi I- General Overview

Maguro (Tuna)

Red Fish

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Order Perciformes, Family Scombridae, Genus Thunnus

A large carnivorous migratory fish positioned high in the food chain. There are eight species in the genus Thunnus worldwide. In Japan, the main species in distribution are Pacific bluefin tuna (Kuromaguro), bigeye tuna (Mebachi), yellowfin tuna (Kihada), and albacore (Bincho), while southern bluefin tuna (Minami-maguro) and Atlantic bluefin tuna are also imported, so a wide variety of tuna is eaten.

Maguro (tuna) refers to fish belonging to the genus Thunnus in the family Scombridae, migratory fish widely distributed across the warm seas of the world. As large carnivorous fish high in the food chain, their population is relatively small. Their bodies are also built for high-speed swimming, sometimes reaching 80 km/h. They swim with their mouths open, taking in oxygen by passing the inflowing seawater over their gills, so if they stop, they suffocate and die. The most prized are the Pacific bluefin tuna and Atlantic bluefin tuna, known as honmaguro, followed by the southern bluefin tuna (Indo-maguro). Honmaguro is called by different names according to size: juveniles are yokowa, those up to about 20 kg are mejimaguro, those around 40 kg are chubo, and those over 100 kg are shibimaguro. The most common everyday tuna in Japan is bigeye tuna (mebachi); generally, "maguro" most often refers to this species, though at high-end restaurants "maguro" often means honmaguro (bluefin). Other everyday tuna include yellowfin tuna (kihada), which is consumed more worldwide than bigeye; albacore (binnaga, also called bincho), which is pink and popular at conveyor-belt sushi where its fatty belly is called bintoro; the small longtail tuna (koshinaga); and the blackfin (Atlantic) tuna (kurohire). While the head, fins, and tail of ordinary fish are discarded, almost all of the tuna is used as prized cuts, including the hachi-no-mi (top of the head), cheek meat, kama (collar), and nakaochi (meat scraped from the bones).

Tuna, a Common Fish of Edo

In the Edo period, tuna was treated as a low-grade fish, cheap and a food of the common people. Toro in particular spoiled easily and was so unpopular that it was said even cats avoided it, but with advances in refrigeration technology and changing tastes, it became a luxury fish some time after World War II. Though a common fish, tuna was very popular among the people of Edo, especially at stall sushi, and the soy-marinated zuke-maguro, which kept longer, was particularly favored. Tuna is often depicted in Edo-period paintings of fish markets, attesting to its popularity.

Tuna being carried through the town of Edo (from

Toro and the Cuts of Tuna

Toro refers to the fatty flesh of tuna. The richest, fattiest part is called otoro, the slightly less fatty part is chutoro, and the rest is akami (lean red meat).
After the head, fins, and tail are removed, the tuna is broken down into four blocks, which are further divided into "kami" (upper), "naka" (middle), and "shimo" (lower). The back side is called "sekami" (upper back), "senaka" (middle back), and "seshimo" (lower back), while the belly side is called "harakami" (upper belly), "haranaka" (middle belly), and "harashimo" (lower belly), and the amount of toro varies depending on the cut.
On the belly, the closer to the kami, the thicker the sinew and the richer the fat, making it expensive. On the back, the fat is roughly even, so the naka with less sinew is more expensive than the kami with stronger sinew, while the shimo, being the part used most in movement, has more sinew and is cheaper.
The amount of toro also varies by species: bluefin and southern bluefin yield a lot of toro, while species such as yellowfin yield almost none. There are also fully farmed tuna that are toro throughout the entire body.