Japanese guide on Sushi grade Tuna Fish | Maguro (マグロ, 鮪)

                by Joost Nusselder | Updated:  December 23, 2020

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The tuna fish (scientific name: Thunnini, a subgrouping of the Scombridae family) is one of the top ocean predators that eat sardines and squid while scouring the open sea.

To satisfy their insatiable desire to consume this ocean “king,” the Japanese would chase the tuna anywhere in the world just to put it on their dinner table – a need so powerful that it transformed the fishing industry dramatically.

a crowd of fishes

It is a story that started in the high economic growth period of the postwar era; however, the art of making tuna-based dishes dates back to ancient Japan.

In the Japanese tongue tuna is called Chūna (チューナ) or Maguro (マグロ, 鮪).

There are currently 7 different kinds of tuna being mainly distributed in Japanese markets. The most sought after varieties of tuna are the high-grade Bluefin tuna (kuromaguro) and the southern bluefin tuna (minamimaguro).

Another crowd favorite is the bigeye tuna (mebachi) which is known for its unique delicious taste due to its fat. The mebachi is caught during autumn and winter seasons as they travel off of the eastern Sea of Japan.

Meanwhile, the albacore tuna (binnaga) is more common in sushi restaurants.

The yellowfin (kihaga) and longtail (koshinaga) tuna are at the bottom end of the hierarchy, but it doesn’t mean that they are any less delicious, because they outsell the other types of tuna in some regions in Japan.

Though all of the seven kinds are tuna, they differ in appearance, production areas, flavor and what dishes they are used for.

The 6 Types of Tuna used for Making Sushi

A Japanese chef once said that he thanks the gods for giving us tuna, otherwise there would be no sushi or sashimi. Pondering on that thought I can relate to what he meant and indeed the taste of tuna is second to none.

Below you will find some of the best tuna species that Japanese chefs use to make sushi and other delicious Japanese cuisines.

Kuromaguro (Bluefin Tuna)

There are two kinds of bluefin tuna found in our oceans and each of them is indigenous to two of the 7 oceans of the world. One is called the Pacific Bluefin Tuna and the other’s name is the Atlantic Bluefin Tuna.

The Japanese fishermen call them both “honmaguro” (top-class tuna) and they are the among all the tuna species that can grow as much as 4 meters in length and weigh up to 600 kg –sometimes more.

The kuromaguro are high-speed swimmers that marine biologists clocked cruising around 80 –90 kph and can travel long distances too! When they are at the juvenile stage chefs call them “meji” or “yokowa” and are mainly eaten as sashimi.

Humans have been interacting with these sea creatures since ancient times and they have been mentioned in the writings of past civilizations around the Mediterranean Sea as part of their diet.

Also the ancient Jomon people of Japan have been using the kuromaguro in their dishes as far back as 16500 years ago!

Today Bluefin tuna are being exported to Japan from other countries as overfishing has grown into an immense problem in our time. As a result, limits on catches and the rearing of eggs and young tuna in artificial methods have been tested.

The Japanese fishermen have determined that the best time to catch Bluefin tuna is during autumn and winter seasons as it accumulates the most fat in its belly.

They call this fat “toro” and is considered a Class A sushi ingredient for its exquisite taste, but its meat is also delicious.

The taste of the tuna also varies depending on the location where the fish was caught.

Also read: the beginners guide to sushi, learn everything about sushi

Minamimaguro (Southern Bluefin Tuna)

Between spring and summer seasons in Japan when the southern bluefin tuna (minamimaguro) migrates to the middle latitudes of the Southern Hemisphere, they gain a lot of fat which is the most delicious part of their body.

It is also called “Indo maguro” (Indian tuna) and it can grow up to 2 meters (6.56 feet) in length and weigh as much as 150 kg.

The southern bluefin tuna is the second largest tuna in the world after the kuromaguro (bluefin tuna).

Prior to the 1980s this fish was widely used including as canned goods; however, the International Union for Conservation of Nature and Natural Resources (IUCN) has prohibited it ever since as overfishing forced them to include it in their Red List of species in danger of extinction.

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On May 20, 1994, more than 7 countries united created the International Union for Conservation of Nature and Natural Resources (IUCN) in order to limit the catch of bluefin tuna to prevent its extinction.

The member countries include:

  1. Australia
  2. The Fishing Entity of Taiwan
  3. Indonesia
  4. Japan
  5. Republic of Korea
  6. New Zealand
  7. South Africa
  8. European Union

As a result, fish stocks are recovering. Presently, nearly all of the minamimaguro caught in the world is used in Japan as part of sashimi’s ingredients. The thinly-sliced flesh of the minamimaguro gives off a strong pleasant flavor and acidic taste.

Once upon a time the word “otoro” (very fatty belly flesh) was exclusively used only for minamimaguro and kuromaguro; today, however, the term means “portions with much fat” and is used in general terms.

Mebachi (Bigeye Tuna)

The mebachi or bigeye tuna is a fish that primarily dwells in the tropical zones and temperate zones of the oceans.

Its main distinct features are its eyes and head, which are out of proportion when compared to its body size and the shape of its body is dumpy as well.

On some rare occasions fishermen have caught a bigeye tuna that weighs over 200 kg, but they mostly normally only grow up to a meter long and weighs at 100 kg max.

According to statistics fishermen make mebachi the second largest catch of tuna type in the world in terms of volume after the yellowfin tuna (kihada).

Mebachi is also the most used tuna type in making sashimi (thinly sliced raw fish). The smaller mebachis are sent to canned fish processing plants after the fishermen catch them.

In recent years, due to the spread of artificial fish aggregating devices (FAD), juvenile mebachi are caught in large quantities by large fishing boats that use encircling nets.

This sparked debates on mebachi overfishing once again and world governments might create new restrictions on fishing mebachi and other tuna species.

Merchants who trade in Japanese fish markets puts a high price on raw mebachi, especially those that are caught in autumn off the Sanriku coast of the Tohoku region.

Mebachi has a particularly bright red meat color. Mebachis have a moderately pronounced flavor, a high fat content (chutoro) with marbling near the skin and a richer flavor than the yellowfin tuna.

Also read: the 9 best sushi sauce recipes for extra flavor

Kihada (Yellowfin Tuna)

At birth the kihada may look just like any other fish, but as it grows older its second back fin and anal fin increase in length and become bright yellow, thus the name.

Its pectoral fin is also long plus they can grow up to 2 meters in length and weigh as much as 200 kg.

Like their cousin the mebachi these fish are commonly found in areas between temperate zones and tropical zones around the world.

About 90% of the catch is accomplished via purse seine fishing, which can bring in quite a number of adult kihadas, but lets the little ones free in order to maintain their population growth.

Before the restriction was placed in tuna meat for manufacturing canned fish prior to the mid-1970s, the kihada was mainly used for that purpose as well as other processed products.

The kihada was re-designated to become key ingredients in making sushi and sashimi after the tuna overfishing ban all thanks to the spreading of quick-freezing facilities and high demand for it in Japanese restaurants.

Kihada is favored in areas west of Nagoya. In west Nagoya, Japan the kihada is favorite seafood and its red meat is refreshing and tasty, especially when the fish is caught during spring and summer seasons.

Binnaga (Albacore Tuna)

The binnaga tuna is the smaller cousin of the other tuna fish previously mentioned, which grows to about 1 meter in length (maximum) and sports a unique very long pectoral fin.

The Japanese called this fish “bin” which means “long hair on both sides of a human face,” although most people call it “bincho” or simply just “long-haired [fish].”

In some regions of Japan it is also referred to as “tonbo” (dragonfly) and this type of tuna often swims in tropical zones and temperate zones of the world’s oceans.

Its pale pink flesh is considered higher-grade compared to those of the bonito and kihada and it is also often used for canned fish manufacturing.

It is also called the “sea chicken” or “white meat” sometimes and its meat becomes even more tender when cooked. Because of that, it is eaten as a fried dish or prepared by meuniere.

Like the other tuna species in this list the binnaga too was re-designated as a key sushi ingredient after the international ban on overfishing of tuna in Earth’s oceans back in the 1970s.

The binnaga’s belly fat is called “bintoro,” which has a light acidic flavor but with strong sweet taste to it.

Koshinaga (Longtail Tuna)

The longtail tuna or the “koshinaga” as the Japanese would call it has a slim body compared to its cousins and it has a particularly longer tail, which it got its name from.

The koshinaga can be found cruising along the waters of Japan, Australia and around the Indian Ocean. It is the smallest among all species of tuna and it usually grows to 50 cm (0.5 meter) in length with occasionally appearing to 1 meter at times.

The longtail tuna has unique white spots on its belly that makes it easier to identify it once caught.

In Japan, the distribution volume of the fish is small as it is not subject to the major fishing industry. However, in the northern Kyushu and Sanin regions, koshinaga is a favorite seafood during autumn as bonito are rarely caught in this part of Japan.

It also has red meat that tastes refreshing and delicious when prepared with various seafood recipes.

The koshinaga is prepared differently in various parts of the world, for example in Australia, it is eaten as steak or a fried dish, while in Indonesia, it is used as an ingredient for curry or is sautéed.

What is Sushi Grade Tuna?

a plate of sashimi and vegetables with soy sauce and chopsticks next to it

Buying raw fish for your personal consumption can be a bit nerve-wrecking, especially if this is the first time you’ll do it. It’s a costly hobby and you would want to make sure that it’s safe to eat it, so here’s a quick-fix guide on how to spot and purchase sushi-grade tuna.

Technically there are no official standards for the “sushi-grade” tuna or fish, although stores may use this label to make their product look impressive to the customers.

The only thing that you need to be careful with is the parasitic fish like the salmon. You have to freeze the fish in order to eliminate all the parasites before you prepare it for consumption.

The flash-freezing technique is known to be the best method to preserve the tuna’s freshness and texture when it is done properly immediately after it’s caught.

The label sushi-grade means that the tuna (or other fish types) is of the highest quality that the store or seller is offering, and the one they are confident is good for raw consumption.

All tunas caught by the fishermen are brought to the Japanese Fish Market and are inspected, graded, and then auctioned by the wholesalers.

The ones deemed by the wholesalers as the best fish meat are given the highest grade, which is 1 and is usually sold to sushi restaurants as sushi-grade tuna.

How to Buy Sushi Grade Fish

It would do you well not to trust all fish meat as “sushi-grade” as not all of them are as what they seem, instead, do your homework and ask questions before making a purchase.

Here are some tips:

  1. Go to the Right Place – When you’re looking for the best fish meat to purchase, always go to a reputable fishmonger or market. Find someone who has a knowledgeable staff, gets in regular shipments, and sells their entire inventory quickly.
  2. Choose Sustainable – Each of us has a symbiotic relationship with this planet including the animals, so if you want to contribute to healthy oceans, then be a responsible consumer. Do a little bit of research to gather information on endangered ocean species and buy only those fish that are not on the Red List to preserve the population of those that are on that list. The Monterey Bay Aquarium Seafood Watch would be a good place to start.
  3. Ask the Right Questions – As a buying customer you have every right to be properly educated and informed about the seafood products that you’re purchasing, so don’t hesitate to ask questions. Ask the wholesaler about where the fish came from, how it was handled, and how long it’s been there. If they process it in their store, then make sure to inquire if the equipment is sanitized to prevent cross-contamination from non-sushi grade fish.
  4. Use Your Senses – Check the fish quality by using your sense of touch and smell. Keep in mind that the fish should always smell like the ocean and if it isn’t, then that means it’s no longer fresh and good for consumption. Ensure that the fish isn’t soft or flaky and it should feature a vibrant color that is very appealing to anyone’s eyes. You choose to skip your purchase and look for a better fish product elsewhere as it isn’t good to consume raw tuna that’s no longer fresh.

You would have to make sure that you consume the fish as soon as it reaches your kitchen as it is a highly perishable item.

Then savor every bite of your sushi-grade fish, whether you use it in sushi, sashimi, ceviche, or crudo!

Tuna Nutrition Facts

Tuna is a great addition to your diet as it is not only affordable, but is also a rich source of omega-3 fatty acids, protein, selenium, and vitamin D.

It’s true that canned tuna alternatives lack the nutritional value that fresh tuna have; however, canned tunas are easier to prepare and are not easily perishable.

The bigeye, yellowfin, and bluefin tunas are commonly sold as frozen meat for sushi restaurants and other high-end bidders, while the albacore and skipjack tuna are primarily used for canned fish production.

The USDA’s nutrition information on tuna meat:

Based on this report we now know that tuna has very low carbohydrates and also has a minuscule amount of fiber or sugar.

Having said that, you may want to supplement your meals with other foods that will make up for what tuna lacks as it may be less filling on its own than other fish.

Also read: this is the sushi eel, did you taste it?

Fat in Tuna

Tuna has very low-fat content, in fact, it only has 2% of the overall fat in the American Heart Association (AHA) recommended daily allowance (RDA), which is 3.5 oz (3/4 cup) yet contains a good amount of omega-3 fatty acids.

Different varieties of tuna have been found to contain different amounts of fat. We’ve listed the different tuna types based on their fat content from most to least fatty: fresh bluefin, canned white albacore tuna, canned light tuna, fresh skipjack tuna, and fresh yellowfin tuna.

Protein in Tuna

Tuna meat has 5 grams of protein for every ounce of it which is a good source of this nutrient aside from other types of meat like poultry, pork or beef.

Normally, a can of tuna contains at least 5 ounces of fish meat, which should give you around 50% of the total RDA for protein in your diet.

Micronutrients in Tuna

Consuming at least 2 ounces of tuna meat will supply about 6% of the RDA for vitamin D and vitamin B6, 15% for vitamin B12, and 4% for iron.

Vitamin D is important to the functioning of your immune system. Meanwhile, the B-vitamins and iron help keep cellular function optimal by releasing and transporting energy from cell to cell.

Health Benefits

The tuna fish species have good omega-3 fatty acids that help keep your heart in good health.

The way these good cholesterols work is that they help decrease the triglycerides in the blood, prevent the risk of developing irregular heartbeats (arrhythmia), and reduce the plaque buildup in the arteries.

The 2 predominant omega-3 fatty acids found in tuna are:

Two ounces of tuna also gets you a whopping 60 percent of your daily recommended amount of selenium/ Another health benefit you’ll get from eating tuna is getting a good amount of selenium.

Eating 2 ounces of tuna a day will give you 60% of the RDA for selenium, this nutrient is important in reproductive and thyroid health, as well as aids in protecting your body from oxidative damage.

Read more: what is Teppanyaki exactly and how do I make it?

Ever had trouble finding Japanese recipes that were easy to make?

We now have "cooking Japanese with ease", our full recipe book and video course with step-by-step tutorials on your favorite recipes.

Joost Nusselder, the founder of Bite My Bun is a content marketer, dad and loves trying out new food with Japanese food at the heart of his passion, and together with his team he's been creating in-depth blog articles since 2016 to help loyal readers with recipes and cooking tips.