We will first explain how the deliciousness of fish is understood scientifically. Then we will explain why fugu (pufferfish or blowfish) is so delicious. In general, the deliciousness of fish, or the taste of fish meat, is thought to be related to four main factors.

(1) The type and content of umami components

(2) The type and content of lipids

(3) Texture

(4) Aroma

When eating fish raw, such as sashimi, factors (1) and (2) are of course important, but (3) is also a very important factor. However, the difficulty with sashimi is that there are big differences in how it is perceived depending on regional differences and individual eating habits. Some people prefer the crunchy texture of fish that has just died and still has some stiffness in the flesh, while others prefer the taste of fish that has been maturing and has a more mature flavor, even if the flesh is soft.

(4) is called orthonasal or retronasal, and we can not only smell the aroma from the tip of our nose but also smell it as it passes from the throat to the nasal cavity while we are chewing the food in our mouth. However, in the case of fish, it seems that ultra-trace chemicals determine the smell, and it is currently impossible to measure it quantitatively. It is also said that there are several hundred thousand types of odor substances, but there are only 400 types of human olfactory receptors. In other words, unlike the sense of taste, which corresponds strictly to specific components, the sense of smell is thought to be a form of gradual pattern recognition. Since various odor components are mixed together, this is also the reason why fish have a complex smell that is rare.

On the premise that the concept of deliciousness is largely subjective, we will look at the question of “what determines the deliciousness of fugu”.

The characteristics of fugu that are often said to make it delicious include “light white flesh,” “the umami increases as it matures,” “low in fat,” “the sashimi has a good texture,” and “fugu is the king of hot pot dishes”. Looking at the data in the Standard Tables of Food Composition in Japan, fugu is outstanding in that it has low-fat content, but in other respects, it does not have any particular umami components that stand out, and the total amount of amino acids is also an average figure.

So where does the umami that is unique to fugu come from?

Generally, the umami content of fish increases when it is matured for half a day to several days after it has died, and this is particularly true of fugu. Let’s take a closer look at the umami content, fat content, and texture of fugu.

① Umami ingredients

The main ingredient that contributes to the deliciousness of fish meat is amino acid, and it is thought that the substances called free amino acids determine the taste. Of the free amino acids, glutamic acid contributes to the umami and sweetness, and when the amount of glycine, alanine, proline, etc. is high, the sweetness is felt more strongly. The sweetness here is different from the sweetness of sugar and is a sensation that can be expressed as the umami, richness, mellowness, and thickness of the taste of the food.

Another important amino acid is Inosinic acid, which is known to act as a flavor enhancer rather than as a taste in itself. The synergistic effect of glutamic acid and inosinic acid on umami has been proven in many foods, such as kelp and bonito flakes. Inosinic acid is almost non-existent in living fish, but after the fish dies, ATP, which acts as an energy source, is broken down, and inosinic acid increases in the fish for a certain period. After cooking a fugu, maturing it for a while has the effect of greatly increasing the amount of Inosinic acid. Although Inosinic acid is an important umami component, it is said to be difficult to quantify for each type of fish because it increases and decreases over time, and there are large individual differences. It is also known that it fluctuates greatly depending on the growth history of the fish, such as what kind of environment it grew up in and what it ate, as well as how it was killed and the stress it was subjected to during the killing process.

② Fat content

The most distinctive feature of fugu from the perspective of food composition is that the fat content of the flesh is extremely low, at less than 1%. While most fish store fat in their flesh as they grow, fugu flesh contains almost no fat. However, this does not mean that fugu has little fat in its body as a whole, and it is known to store a lot of fat in its internal organs such as the testes and liver. The detailed mechanism is not known except that it is related to factors involved in lipid accumulation, but the distribution of fat in the body of fugu is different from that of other fish.

Among the fats in fish, the important ones for sensing taste are the omega-3 polyunsaturated fatty acids such as EPA and DHA, one type of so-called long-chain fatty acids. These have a low melting point, so they melt quickly on the tongue and spread easily, affecting the richness and fullness of the taste and the smoothness of the texture on the tongue.

As you can see, while fish fat has some positive aspects, it also has some negative ones, such as greasy. In the case of fugu, the fact that it has little fat in its flesh is thought to have two main advantages.

One is that the fat makes it harder for umami ingredients such as amino acids to be masked. This is strongly suggested by the structure of the human tongue. For example, if the lean meat and fatty meat of tuna have the same level of deliciousness, the lean meat will have a stronger umami taste, but the fatty meat will tend to have a stronger fat taste than umami (research results show that fat itself has no taste). As there is almost no fat in the meat of fugu, it is thought that the umami of the fish meat can be directly tasted.

Another important point is that it is not easily affected by the oxidation of fat. One of the umami components, Inosinic acid, increases after the fish has died, but before the Inosinic acid has increased sufficiently, the long-chain fatty acids oxidize quickly, causing the unpleasant smell known as “fishy smell” to appear and the color to change, spoiling the taste. In contrast, the meat of the fugu contains very little fat, so you can take your time maturing it slowly without worrying about the oxidation of the fat, and bring out the umami components.

③ Texture

Of all the fish, fugu has the hardest flesh. What is particularly worth noting is the unique crunchiness when eaten raw, such as in sashimi, and the hardness of the flesh when chewed. The crunchiness of fish meat is determined by the way the myofibrillar proteins (actin and myosin) that make up the muscles are connected, and also by the type and content of the connective tissue proteins (mainly collagen) that connect them.

Looking at collagen, it is said that the flesh of fugu contains more than double the amount of collagen compared to common fish such as red　seabream and sardines. This is why it has a firm texture, and it is possible to make sashimi that is so thin that it is almost transparent. On the other hand, it could also be interpreted that it is too hard to eat unless it is cut thinly.

In addition to the high collagen content, it has also been found that the rate at which the flesh of fugu softens after the rigor mortis has dissipated is slower than any other fish. In general, the flesh of fish becomes softer after rigor mortis has dissipated, but this is related to the decrease in type V collagen. It is said that the solubilization of collagen in fugu is less than that of other fish, so even after death, when some degree of maturing has occurred and a large amount of inosinic acid has accumulated, it still has sufficient firmness to be eaten as sashimi in thin slices. In this respect, too, fugu is suited to maturing.

Incidentally, collagen itself is just connective tissue, so it has almost no taste. Also, the proteins that contain collagen will denature when heated, so when you eat it after heating it, you will enjoy the soft texture rather than the crunchiness.

Before we come to our conclusion, we would like to inform you of the current situation surrounding fugu so that you do not misunderstand it as a fish that endangers your life. Between 2014 and 2023, there were 235 cases of food poisoning caused by fugu, and 5 of these people died. Most of these cases were caused by amateur cooks who lacked the necessary expertise and skills. Fugu poison is colorless, tasteless, and odorless. Therefore, it is impossible to tell whether or not fugu poison is present by sensory means. In addition, the fugu poison is highly heat-resistant and cannot be detoxified using ordinary cooking methods. For this reason, fugu must be prepared by someone with specialist knowledge and skills and a cooking license. Conversely, you can just eat it at a restaurant that specializes in fugu.

To conclude, in the case of fugu, the umami component increases over time, and the fact that the flesh contains little fat means that it is less likely to oxidize, and the fact that it retains sufficient firmness means that it is easier to perceive the umami than with any other fish. And even when heat is applied, the combination of the moderate elasticity and the dashi produced by the other ingredients results in an unparalleled taste. This can be said to be the fundamental part of the deliciousness of fugu.

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Fusenkinme (Red bream) is occasionally caught along with Splendid alfonsino (Kinmedai). Until recently, they were considered to be the same species. Kinmedai has elongated slit-like posterior nostrils, while Fusenkinme has oval-shaped posterior nostrils. Kinmedai can grow over 50 cm long, whereas Fusenkinme stops at 40 cm.

Fusenkinme is fattier than Kinmedai and is called Aburakinme or Torokinme by fishermen, in areas that distinguish between Fusenkinme and Kinmedai, there is a difference in market price, but it is rarely distributed and is consumed locally.

Torokinme does not refer to the belly part of Kinmedai but to Fusenkinme, a rare species of Kinmedai. Incidentally, three Kinmedai, Nanyokinme, and Fusenkinme species are distributed in Japan.

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What is the thought behind Toro?

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Consumers are inevitably confused by the word Toro. It isn’t easy to separate the word from a mere marketing term. Therefore, the market contains fish names with Toro as a prefix.

Torokarei (karei means flounder) is a trade name for a fish named after the toro of tuna, which has a rich, tender texture, and is an arrowtooth halibut (Aburakarei).

Aburakarei is distributed north of Choshi, the northern Sea of Japan, the Sea of Okhotsk, and the western Bering Sea. Aburakarei is a typical eating fish among flounder species, and unfortunately, it is considered the most tasteless and has low commercial value. Black halibut (Karasugare), a relatively tasty and inexpensive fish, has become expensive, so perhaps it is Aburakarei’s turn.

So a name that would sell was needed, so it became Torokarei.

In recent years, Aburakarei has been imported from the U.S. and other countries in large quantities of fillets processed for frying. It is inexpensive and its distribution is stable. Aburakarei is characterized by its meat containing so much fat that it melts when heated. Even when heated, the flesh remains tender, and it is often used overseas for frying as fish and chips. The most common type of engawa at conveyor-belt sushi restaurants is either Aburagarei or Karasugarei.

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What is Largescale blackfish (Mejina)?

Largescale blackfish (Mejina) is distributed throughout Japan south of southern Hokkaido, Taiwan, and the East China Sea. Its bodies are oval and flattened, and its body color is blackish purple. It is diurnal and forms schools, moving to deeper waters offshore as it grows.

It can grow up to 60 cm in length, but most of those on the market are about 40 cm in length. In summer, it feeds on animal food such as small shrimps, and in winter, it prefers vegetable food such as seaweed and nori, which means that the season is winter, as the fish’s smell of the sea disappears and it becomes fatty during the winter.

The name of this species in the Kansai region is “Gure,” and it is a popular rock-fishing target. Its scientific name is Girella punctata Gray, 1835.

What does Largescale blackfish (Mejina) sushi taste like?

Largescale blackfish (Mejina) looks like red seabream (Tai), but are related to Japanese sea bass (Suzuki). The Kuromejina (Girella leonina (Richardson,1846)) and Okinamejina (Girella mezina Jordan & Starks, 1907) are members of the Mejina family, but the Mejina has the best taste.

It can be served as sashimi, grilled, simmered, or even cooked in a pot. It is relatively easy to cook because it is well suited to cooking methods that use oil. If the gall bladder is accidentally broken, a strong odor can be passed around in the air, which can make it smell even worse. Therefore, it is important to avoid damaging the internal organs when cooking it.

It is inexpensive, but because it is not caught in large numbers, it is not always available at sushi restaurants. Its flesh is a beautiful pale pink color, which is hard to imagine from the black body surface.

In winter, it has a stronger taste than red seabream, with the fat coming in closer to the mouth and a stronger umami. In the summer, it can have a slightly peculiar aroma, so it is best to yubiki (parboil) or broil the fish before serving it as nigiri sushi.

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Revision date: June 12, 2023

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What is Black scraper (Umazurahagi)?

Black scraper (Umazurahagi) is distributed in the Sea of Japan from Hokkaido to Kyushu, the Pacific Ocean, the Yellow Sea, and the East China Sea from the Korean Peninsula to the coast of China. It is a familiar fish caught throughout Japan. Umazurahagi are called nagahagi (naga means long) because they are longer than Filefish (Kawahagi).

They are abundant at depths of around 10m, slightly offshore from Filefish. When young, around 10 cm in length, they migrate in schools, but as adults, they are often found alone. Adults gather in coastal areas to spawn from around May to July and dive to deeper water around November.

They are omnivores, feeding on benthic organisms such as seaweeds, crustaceans, polychaetes, and even jellyfish. Its scientific name is Thamnaconus modestus (Gunther,1877).

What does Black scraper (Umazurahagi) sushi taste like?

Black scraper (Umazurahagi) has a blurry appearance and does not look tasty, but once peeled, it reveals a clear white flesh similar to that of pufferfish.

The price of Umazurahagi is completely different between those caught in large quantities by bottom trawling fishing and those caught by pole and line fishing. Therefore, Ikejime or live fish are used for sushi toppings.

The liver, with its rich flavor, can be raw or seared and used in nigiri sushi to make an exceptional dish. Although it is looked down upon compared to Filefish and pufferfish, it is relatively affordable and highly regarded as a topping, and is not a substitute for Filefish at all.

However, the quantity of fish received at the Toyosu market and other markets is not stable. From that point of view, few restaurants offer nigiri sushi.

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Revision date: June 6, 2023

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What is Marbled rockfish (Kasago)?

Marbled rockfish (Kasago) can be found anywhere along the coast from southern Hokkaido to the East China Sea. It lives in the shadows of reefs and blocks from the coast to depths of about 60m to 200m. A voracious carnivorous fish, it preys on crustaceans such as small shrimps, polychaetes such as ragworm, and small fish such as gobies.

Body color varies from dark brown, reddish, to blackish, and there is a great deal of variation depending on the environment in which they live. Those that inhabit deeper water are said to be redder, while those that inhabit shallower water are said to be darker. Another characteristic of this species is the irregular white patches on its back side.

Along with Mebaru and Ainame, it is a representative of rockfish (It is a fish that does not migrate far and has a small habitat). It is about 30 cm long. Its scientific name is Sebastiscus marmoratus (Cuvier, 1829).

Some species of marbled rockfish have poison lines on their pectoral fins and dorsal fins, so care should be taken when cooking them. Also, since they have many spines all over their body, when grabbing a live fish, put your thumb in their mouth and grasp their lower jaw.

It is generally considered a winter fish, but the season is spring. It is most fatty from January to April, and the black ones that inhabit the seashore are said to be tastier than the reddish marbled rockfish that inhabit offshore waters. It can be caught in all regions of the Japanese archipelago, which stretches from north to south, a light white fish that is easy to remove from the bone, so it is delicious regardless of the season. The larger ones are often made into sashimi or sushi, while the smaller ones are often eaten as boiled fish.

What is Marbled rockfish (Kasago) sushi taste like?

Marbled rockfish (Kasago) is treated as a high-end fish in the Toyosu market, but the supply is not consistent. In addition, its large head and low yield make it rare for restaurants to serve nigiri sushi and sashimi.

The elegant flavor of nigiri sushi and sashimi is, to put it mildly, unsatisfying. The best way to eat nigiri is to broil the skin and let the aroma come out. This will dissolve the gelatinous material under the skin, and the sweetness and umami of the fat can be felt gradually. It is also good to eat it with citrus fruits such as sudachi and salt.

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Revision date: May 27, 2023

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What is Rockfish (Mebaru)?

Rockfish (Mebaru) are distributed over a relatively wide area from southern Hokkaido to Kyushu, the Korean Peninsula, and elsewhere. They inhabit rocky reefs at depths of 50 to 150 meters. The length of the fish is 20-25 cm.

There are several species of rockfish (Mebaru): Aka-mebaru (Sebastes inermis Cuvier,1829), Kuro-mebaru (Sebastes ventricosus Temminck and Schlegel,1843), and Shiro-mebaru (Sebastes cheni Barsukov,1988), which are generally called mebaru. However, the three species are so similar in appearance that it is difficult to distinguish them at a glance.

The fish is caught by pole-and-line and longline fishing starting around March, and becomes fat and oily by April when the water temperature begins to rise. Anglers are most likely to catch Kuro-mebaru. They are mainly eaten simmered or grilled.

However, the fish is poisonous in its dorsal fin, so it is important to be very careful when handling it. Because it is a very small amount of poison, it is a cause that is neglected, but there are times when serious symptoms appear.

What does Goldeye rockfish (Usumebaru) sushi taste like?

Sushi chefs use a species called Goldeye rockfish (Usumebaru), which is found in deeper waters offshore. The maximum length of the fish is 35 cm. The main production areas are Aomori and Yamagata prefectures.

Goldeye rockfish is a member of the scorpionfish family, but it is less fishy than scorpionfish and has a very light flavor with firm flesh. It has little fat and a light aftertaste, making it a good pairing with sushi rice. When served as nigiri sushi, it is also good to use Kobujime. Although the market availability is stable, it is traded at a high price.

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Revision date: May 26, 2023

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What is Barfin flounder (Matsukawagarei)?

Barfin flounder (Matsukawagarei) is distributed along the Pacific coast north of Ibaraki Prefecture and in the Sea of Japan north of Toyama Prefecture, the southern Sea of Okhotsk, and the Kurile Islands. It inhabits sandy muddy areas at depths of up to 200 m, feeding mainly on crustaceans and small fishes. The maximum length of the body is 80 cm.

It is similar in appearance to the closely related Spotted halibut, but the Barfin flounder has banded black spots on its fins, while the Spotted halibut has circular ones. The name ” Matsukawagarei ” is said to come from its scales, which are hard and resemble the epidermis of a pine tree. Barfin flounder is now very rare in the wild, and most of the fish caught are released juveniles. This is based on the habit of flounder species to remain in the waters where they are released. The main production areas are Hokkaido, Aomori, and Iwate prefectures, and the season is winter. The scientific name is Verasper moseri Jordan & Gilbert, 1898.

What does Barfin flounder (Matsukawagarei) sushi taste like?

Barfin flounder (Matsukawagarei) tastes better in larger sizes, and the males are tastier than the females. Its flesh is firm, and when fresh, it tastes better when thinly sliced. The umami increases after about two days of maturing, as is the case with other flounders.

Barfin flounder, along with spotted halibut, is a high-end fish, and if asked which is more delicious, barfin flounder or spotted halibut, most people would probably say spotted halibut. However, the reason may be that they are not familiar with Barfin flounder. As proof of this, you will almost never see it at high-end sushi restaurants in Tokyo, but it is not that uncommon at high-end restaurants in Sapporo.

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Revision date: May 9, 2023

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What is Spotted knifejaw (Ishigakidai)?

Spotted knifejaw (Ishigakidai) is distributed along the Pacific coast south of Ibaraki Prefecture and along the Sea of Japan south of Yamaguchi Prefecture to the South China Sea. It inhabits mainly rocky reefs. The length of the body reaches 90 cm.

The ecology and habits are similar to those of Barred knifejaw (Ishidai), but young fish are generally brownish with numerous blackish-brown stone wall (stone wall is ishigaki in Japanese) patterns scattered throughout the body. As the fish grows, the pattern becomes lighter, and in male adults it disappears completely. The season is summer.

Note that some of the larger Barred knifejaw and Spotted knifejaw (over 60 cm) may have Ciguatera poisoning. The scientific name is Oplegnathus punctatus (Temminck and Schlegel, 1844).

What does Spotted knifejaw (Ishigakidai) sushi taste like?

The meat of Spotted knifejaw (Ishigakidai) is firmer and tighter than that of Red seabream (Madai), and it is so chewy that it feels too hard to make sashimi if it has just died. Therefore, like puffer fish, usuzukuri (thinly sliced) is used for sashimi and sushi topping.

Spotted knifejaw has a more subtle scent of the sea than barred knifejaw. The color of chiai (dark red meat) is not a bright red, but rather a duller shade, but the meat is surprisingly fatty and delicious.

Nigiri sushi is also good with salt and kabosu. Its umami is thought to arise from eating sea urchins, shellfish and crustaceans. Both nigiri sushi and sashimi are rare in Tokyo, but common in Shikoku and Kyushu.

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Revision date: April 26, 2023

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What is Silver croaker (Ishimochi)?

Silver croaker (Ishimochi or Shiroguchi) is distributed in the Tohoku region and southwards, the East China Sea, the Indian Ocean, and the western Pacific Ocean. It is mainly found on sandy mud bottoms at depths of 20~140m. Its body color is shiny silvery white with somewhat indistinct black spots on the tops of its gill covers. The Japanese name Ishimochi (Ishimochi means having the stones) is derived from the presence of large calcareous otoliths within the skull bones. The length of the body is about 40 cm. The season is summer. Caught in large quantities in the East China Sea by bottom trawl fishing, it is mainly used as a raw material for high-grade fish paste. The scientific name is Pennahia argentata (Houttuyn,1782).

What does Silver croaker (Ishimochi) sushi taste like?

Silver croaker (Ishimochi) can be eaten raw if fresh, and it goes well with vinegared rice. Its clear white flesh has a firm texture, but it is somewhat watery, so it is best served as sujime or yubiki.

There are many delicious white fish, but in terms of individuality, Silver croaker may be the top level among sushi toppings. Conversely, I am once again impressed by the power of vinegared rice that catches the peculiarities of Silver croaker. In the Kanto region, it is a popular fish for salted grilled fish, and it takes on a completely different flavor when grilled.

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Revision date: April 19, 2023

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