Edomaesushi | Sushiblog－Sushiuniversity

What is Shiromi?

Hirame is a high-quality fish that goes for at least US $50 per kilogram. It can even exceed US $80 per kilogram, depending on the timing and the fish’s body.

Hirame is a typical shiromi (white meat fish) when winter is approaching and a great sushi topping to start off a meal. Also, the taste is so delicate that the original flavor can be cancelled out just by adding too much soy sauce. How the chef expresses this delicate taste is a tribute to his skill and something that foodies look forward to.

In the US, Hirame is often written as “halibut” on the menu of sushi restaurants. Technically the English name of Hirame is Bastard halibut. Hailbut (referring to Pacific halibut) is called “Ohyo” in Japanese. In Japan, the engawa of massive Ohyo is often used as a substitute for Hirame engawa at conveyor belt sushi, but the two are not confused for each other. There is no mistake that Hirame is related to halibut, but they are completely different species. Incidentally, the price of Ohyo is US $3 to $20 per kilogram. It is incomparably cheaper than Hirame.

Also, depending on the restaurant it may be represented in a variety of other ways such as fluke, flatfish and flounder. These terms refer to relatives of Hirame (鮃) or Karei (鰈), but do not indicate any certain species of fish. In other words, there is generally no distinction between Hirame and Karei in the US and to go even further, all white fish are thought to be the same species.

The delicious taste of fish is dependent on the distribution of fat and the amount of inosinic acid. Therefore, fish taste better in the seasons when they have fattened up. On the other hand, people have a hard time distinguishing between types of fish when comparing the tastes of the parts with less fat. The free amino acids in fish meat differ only slightly between different types of fish. In other words, the flavor of all fish is mostly the same. It is only the amount of fat and the amount of the umami component, inosinic acid, that differ between fish, so apparently even sushi chefs cannot distinguish between fish just by eating the back part, which has a low fat content.

This is part of the reason why in the US all white fish is all lumped into the same category and to top it off, the common consensus there is that white fish has no flavor.

At sushi restaurants in Japan, generally there are at least two types of white fish on offer. It is practically guaranteed that Hirame will be in stock in winter. The light flavor unique to this white meat that spreads with each bite maximizes the aroma and sweetness of the vinegared rice. Recently, white fish with high levels of fat such as Kinmedai and Nodoguro, have become standard, high-quality white fish.

The difference between how even these sorts of white fish are handled in the US and Japan is astonishing. That said, flavorless Hirame is not consumed as sashimi or sushi even in Japan. It is served in dishes with strong flavors, like carpaccio. It’s possible that delicious Hirame is just not available in the US.

Related contents: List of White flesh fish

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Revision date: July 16, 2022

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There are strangely two types of Ama ebi

It goes without saying, that each type of fish has its very own scientific name. However, in places like the Toyosu Fish Market, there are seafoods that end up sharing a name.

The official Japanese name of ama ebi (sweet shrimp) is “Hokkoku Akaebi” (scientific name: Pandaluseous Makarov).

In Japan, ama ebi lives naturally along the Sea of Japan coast and the coasts of Hokkaido, and the ama ebi sold at Toyosu market is caught from Toyama prefecture and northward to Hokkaido and southward. When made into nigiri sushi, it is harmonious with the acidity of the vinegared rice and the thick sweetness is irresistible. It really lives up to its “sweet” name.

However, what dominates the Toyosu Market is frozen shrimp of the same pandalidae family, called “Honhokkoku Akaebi” (scientific name: pandalus borealis kroyer) from Iceland and Greenland.

This is distributed as “Ama ebi” at the market, but strictly speaking it is a different type of shrimp. As far as appearance goes, it is impossible to tell the difference and they say that even the flavor is the same.

The majority of ama ebi used at conveyor belt sushi is produced in Greenland and imported to Japan through China. The reason for this import circumvention is that the processing to turn the shrimp into ready-made sushi toppings is done using inexpensive labor in China. The frozen ama ebi is thawed in China, processed (head, shell, etc., are removed) and then frozen again. Of course, this process diminishes the freshness of the fish. Preservatives are used to help prevent this. For example, pigment fixing agents are used in order to reduce discoloration from fading. Furthermore, acidity regulators and antioxidants are used to prevent changes in the quality and color of the meat. Ama ebi is stored in packs of 50, imported en masse to Japan, and can be used for sushi or sashimi immediately upon thawing.

As this ama ebi caught in the North Atlantic Ocean is considerably cheaper than domestic ama ebi, the reality is that conveyor belt sushi wouldn’t survive in Japan without these imports.

What is Masuzushi?

The origin of Masuzushi dates back about 300 years. Apparently, in 1717 it was first presented as Ayu narezushi (narezushi is a traditional food, said to be the original form of sushi and made from lactic fermentation of fish) to the third-generation feudal lord, Toshioki Maeda, by Shinpachi Yoshimura, a feudal retainer of Toyama who excelled in cooking skills. Toshioki liked the dish very much and assigned the role of vinegaring Ayu to Shinpachi. After that, it is said that the same narezushi was presented to the eighth shogun of the Tokugawa shogunate, Yoshimune Tokugawa, and that Yoshimune was extremely pleased with it.

Shinpachi’s ayuzushi was made through the painstaking process of washing salt-preserved ayu with sake, then pickling it for around 12 days, removing the rice the day before it was to be served, then adding new rice that had been flavored with sake and salt.

This transformed to the present-day Masuzushi in the late Edo period, when the amount of vinegar was increased. Hayazushi, in which vinegar is added to rice for a quick meal, became popular, and Sakuramasu started to be used instead of Ayu, These factors seem to have contributed to how it transformed into the Masuzushi we see today.

It is made by first filleting fresh Sakuramasu into three pieces and removing the skin and bones, then cutting into 3 mm thick strips. These strips are sprinkled with salt and left for 3 to 5 hours before being washed with a vinegar mixture made of salt, sugar and other seasonings (water is never used for this). The type and amount of seasonings mixed with the vinegar at this time is a secret and determines the house flavor of the restaurant or family. Sakuramasu that has marinated for 1 to 2 hours in the vinegar mixture is placed on sushi rice in the container, then held down with weights to press for several hours to complete the Masuzushi.

Long ago, it was only made with Sakuramasu caught in Jinzu River, so it was made between April and July. However, due to reasons such as a dam being built upstream and water pollution, Sakuramasu produced outside the prefecture and imported Masu (trout) is used now, and it is made year-round.

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Revision date: August 3, 2021

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What is Funazushi?

Narezushi (mainly a preserved food in which fish undergoes lactic fermentation with salt and rice), in which Sushi finds its roots, can still be found even today throughout Japan. The most famous is Funazushi (鮒寿司, 鮒鮓, 鮒寿し) in Shiga prefecture.

Although it has “sushi” in the name, according to common knowledge of the day, it would be called crucian carp. The sweet and sour smell tickles your nose and it’s almost like pickled crucian carp. When you actually put it in your mouth it fills with an intense sourness and it can only be described as a really sour pickled food. However, the more you eat it, the more you somehow get used to it and in the end it becomes a favorite food that you will even crave. This effect is so mysterious that people even wonder, “Could this have been synchronized at some point with the tastes of our Japanese ancestors?”

Making Funazushi sushi is surprisingly simple. The only ingredients are crucian carp caught in Lake Biwa, rice and salt. First the internal organs are removed from the crucian carp, next it is salted and then it is shade-dried. This crucian carp is packed tightly into freshly steamed rice in a large cask. “Sushizume” refers to this precise situation, and the ingredients are packed in so there is no air inside. If air is let in, the oxygen will cause microbiota to grow. In other words, it will rot. This is the most important thing in making funazushi.

While this cask is left for eight months to two years, special microorganisms will cultivate even without oxygen. These are lactic bacteria and acetic bacteria, which work to change the entire contents into a sour flavor.

After that, the mushy rice is removed from the finished Funazushi, and only the crucian carp is consumed. However, let me reiterate, this sour flavor is intense and complicated. Comparing it to bleu cheese or camembert cheese might make it easier to understand. The taste is so intense that it makes some people sick.

Incidentally, there are records from when Hideyoshi Toyotomi advanced his army to the Korean peninsula (around 1592), that Funazushi from Oumi was presented to soldiers on the front line as a comfort food. This episode illustrates the fact that Funazushi was a dish of pride for the people of the town of Nagahama (where Toyotomi’s castle was located, now part of Shiga prefecture).

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Revision date: June 23, 2023

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What is Yamawasabi?

Horseradish is believed to have originated in Eastern Europe. It’s a cruciferous vegetable, alongside mustard, wasabi, cabbage, and broccoli. Horseradish is very fertile, and buds and roots will sprout just by cutting the root stock part to an appropriate size and soaking it in water. Once transferred to soil the roots will multiply quickly even without any other efforts.

In Europe horseradish is used as an ingredient for sauces or to accompany sausage and roast beef, or as a subtle seasoning for other dishes. In Japan most is used as an ingredient in processed foods such as wasabi powder or wasabi paste. Unlike wasabi, horseradish is characterized by its pure white root and strong spicy flavor. In Hokkaido horseradish is called “Yamawasabi” and is a common sight at home dinner tables.

Farming of Yamawasabi for food started in the Meiji era and settled in Hokkaido. Currently over 90% of the domestic production in Japan is accounted for in Hokkaido. While it is grown throughout Hokkaido, the vast Yamawasabi fields befitting Hokkaido are especially prevalent in Abashiri and Kitami.

In Hokkaido, Yamawasabi is eaten as an accompaniment to white rice. Grated Yamawasabi is sprinkled on rice and there are also jars of “Soy sauce-marinated Yamawasabi” sold as a normal item at supermarkets. Besides on rice, it is also indispensable to Hokkaido cuisine as seasoning for hiyayakko (cold tofu) and sashimi.

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Revision date: June 28, 2021

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What is Rendaku?

In Japanese, when a compound word is made out of two individual words, and the first consonant of the second word changes from a “clear sound” to a “fuzzy sound”, it is called “Rendaku”. For example, Edomae (江戸前) + sushi (寿司) changes to Edomaezushi (江戸前寿司). However, the correct pronunciation is only generalized among Japanese people, so in this book we chose the most commonly searched version of each compound word.

Examples of Rendaku (連濁):

Nigiri (握り) + sushi (寿司)→Nigirizushi (握り寿司)

Inari (稲荷) + sushi (寿司)→Inarizushi (稲荷寿司)

Masu (鱒) + sushi (寿司)→Masuzushi (鱒寿司)

Kaiten (回転) + sushi (寿司)→Kaitenzushi (回転寿司)

Kuro (黒) + tai (鯛)→Kurodai (黒鯛)

Ma (真) + tako (蛸)→Madako (真蛸)

Aka (赤) + kai (貝)→Akagai (赤貝)

Tori (鳥) + kai (貝)→Torigai (鳥貝)

Shiromi (白身) + sakana (魚)→Shiromizakana (白身魚)

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Revision date: June 9, 2021

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What is Shiojime?

Generally, saltwater fish grow in seawater, and their bodies naturally contain a certain concentration of salt. Because seawater has a higher salinity than the fish’s internal fluids, the water in their bodies is constantly being drawn out by osmotic pressure. As this water is lost, the internal salt concentration increases. To compensate, saltwater fish actively drink large amounts of seawater and excrete the excess salt through specialized cells in their gills and kidneys. This complex osmoregulation mechanism helps them maintain a balance, which is why their flesh typically contains a high percentage of water.

This high moisture content sometimes gives the impression that the fish is “somehow watery” or lacking in firmness. However, once the fish is cooked—especially through gentle heating—the texture becomes soft and fluffy, enhancing its natural qualities.

Therefore, when preparing fish for cooking, it is often sprinkled with salt approximately 30 minutes to one hour beforehand. This process, commonly practiced by sushi chefs as well, is called Shiojime (塩締め), or salting.

Shiojime serves several purposes. First, it draws out excess moisture through the process of osmosis, which in turn concentrates the fish’s natural umami (savory) flavor.

Additionally, by removing moisture, Shiojime helps eliminate the fishy odor (commonly caused by compounds like trimethylamine), allowing the clean, delicate flavor of the fish to shine through.

Another important benefit of Shiojime is that it helps control bacteria. When salt is applied to the fish, it creates a salty (hypertonic) environment that draws water out of the bacteria on the surface. Without enough water, the bacteria can’t survive or grow. In addition, salt lowers the water activity in the fish, which makes it harder for microbes to multiply. This helps keep the fish safe to eat and slows down spoilage, making it last longer.

In traditional sushi preparation, Shiojime is often followed by Sujime (vinegar curing). The amount of vinegar that penetrates the fish depends significantly on the prior conditions established during Shiojime, making it a delicate and finely tuned process that requires experience and attention to detail.

Ultimately, Shiojime is a time-honored technique that delivers numerous benefits—enhancing flavor, improving texture, reducing odors, and increasing safety—while showcasing the depth of Japanese culinary knowledge.

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Revision date: June 12, 2025

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What is Karami?

Sashimi essentials such as wasabi, ginger, karami-daikon, etc., are collectively called “Karami”. The term Karami comes from the Japanese word 辛味, which literally means “spicy” or “pungent taste.” In the context of sashimi, it refers not to intense heat like chili peppers, but to a sharp, aromatic pungency that stimulates the palate, cuts through richness, and neutralizes fishy odors. This quality is why karami ingredients—such as wasabi, ginger, or grated daikon—are used alongside raw fish: they enhance flavor while making the dish feel cleaner and more refreshing.

Originally Karami was a type of Tsuma. From the mid to late Edo period, Karashi (mustard) was mainly used for karami in sashimi. Eventually, due to the influence of Edomae sushi, wasabi became the norm. Wasabi was favored not only for its refreshing heat but also for its antibacterial properties and its ability to complement the delicate flavors of raw fish. For sashimi such as bonito and sardines, wasabi isn’t enough to offset the peculiar aroma. In some cases, it is better to use ginger, which works on the root components of the odor. These types of fish have the best flavor once spring has passed, and interestingly enough, wasabi is least prevalent in summertime, while ginger is in peak season. Mother nature seems to know what she’s doing.

Historically, karami was considered a type of tsuma, but today it is classified as a type of yakumi (condiment). Tsuma refers to the decorative and edible garnishes that accompany sashimi, serving both aesthetic and functional purposes—enhancing presentation, adding contrasting textures, and refreshing the palate between bites. Over time, karami came to be recognized not just as a garnish but as a form of yakumi (condiment), whose primary role is to add flavor, mask unwanted odors, and balance the taste of the fish rather than to decorate the plate.

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Revision date: August 12, 2025

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What is Mazuma wasabi?

So, what is the true meaning of the shocking phrase, “Once you try tuna or flounder with this wasabi, you’ll never be able to eat it without wasabi again”?

Wasabi is assessed by five points: its coloring, fragrance, stickiness, spiciness and sweetness. So does that mean this wasabi gets the highest marks for all these categories? In other words, when wasabi is grated, it’s a bright green color. The fragrance is fresh. It has a strong stickiness. The spiciness has a punch. After some time, it has a delicate sweetness.

The glorious thing about wasabi is that the vivid spiciness that goes through to the tip of your nose never lingers on your tongue or in your mouth. This lack of aftertaste is the biggest feature of wasabi’s delicious taste. The tastes of sashimi and sushi are subtle and delicate. Each cut of fish and each piece of sushi has its own unique and enjoyable flavor. If the wasabi were to linger on your tongue or in your mouth, it would get in the way of the next, new taste.

Furthermore, the potency of this spiciness is not what makes wasabi taste good. Good wasabi is spicy, but it also has a premium sweetness and refreshing fragrance at the same time. This is the true delicious taste of wasabi and it is a specific characteristic. Therefore, it is a superb spice for making good fish even more delicious.

Wasabi is native to the Japanese Islands and Sakhalin, Russia, is a perennial plant that belongs to the Brassicaceae family and is bred both by dividing roots for replanting and from seeds. The potato-shaped part that is normally grated and consumed, is part of the wasabi’s stem and called rhizome, just as potatoes have subterranean stems. Wasabi is broadly divided into red stem, which has a high anthocyanin content in the stems and blue stem, which has a low anthocyanin content. Mazuma (red stem), daruma (blue stem) and Shimane No. 3 (blue stem) are the three major types and it is known that most varieties that are currently cultivated were improved breeding from these. During the Edo period, daruma wasabi that was cultivated in Shizuoka was the most common, but then mazuma was introduced and became widespread, perhaps from degradation due to about 40 years of cultivation. Currently, mazuma seed cultivation only makes up about 30% of the total wasabi, even in Shizuoka, because the cultivation period of mazuma is longer than the seedling type and suitable places for planting have decreased, among other reasons.

The external appearance of mazuma is a dark green color and since there is purple on the base of the leaf, they are easy to distinguish by appearance alone. Since mazuma seeds mostly don’t fruit, the seedlings are cultivated by dividing the roots. It is difficult to ensure high quantity by dividing roots. Furthermore, it takes time to grow, so there is inevitably a rarity value.

The protrusions that occur with the growth of the surface are small and grow very close together, arranged in a spiral shape. This is the best wasabi of which the spiciness includes sufficient sweetness and that has a refreshing fragrance. On the market, it goes for US $50 to $200 per kilogram. Of course, it depends on the size, but one plant goes for about US $20. Wasabi is mainly produced on the Izu peninsula right now, but Yugashima, Amagi and Gotemba are known for mazuma. However, mazuma is actually native to Wakayama prefecture. It started in the Kawamata area of Inami Town in Wakayama, formerly known as Mazuma Village.

What is the trick to super cheap Ikura at conveyor belt sushi restaurants?

Immature salmon eggs still wrapped in ovarian membrane and salted are called sujiko. Ikura is salmon roe in which each mature egg is separated from the ovarian membrane before laying the eggs and then salted or marinated in soy sauce. The ikura of Chum salmon going upstream in the Kushiro River and Tokachi River in Hokkaido From October to December are considered to be premium ikura.

For cheap ikura, roe broken up inside the ovarian membrane in a fish that is approaching spawning time called “barako” is used. When the ovarian membrane of barako is torn, the eggs will fall out and scatter, so while they don’t take much work to prepare for serving, they also don’t taste particularly good. Even cats turn up their noses at barako, so they are also called “neko-matagi”, which literally means “the cat walks over it” and is used to refer to unpalatable fish. However, each egg is large and they look very appealing, so they are used at higher-end conveyor belt sushi. Unlike the 100-yen (US $1) restaurants, these higher-end restaurants don’t use disguised fish or substitute fish. This is because their basic business strategy is to differentiate themselves by attracting customers with authentic toppings. Generally they market the high quality of their toppings, but the ikura is actually this cheap “neko-matagi”.

Beneath this strategy of attracting customers with authentic toppings is this “Deceptive business strategy”. Salmon also swims upstream in the rivers of Tohoku and Hokuriku. However, the taste of ikura tastes inferior to that in Hokkaido. This ikura is also served at the higher end restaurants. That’s because although it doesn’t taste as good, it’s orthodox ikura. In case of orthodox ikura, the roe is used within one hour of the catch. But, if time passes and the freshness drops, the eggs will dry out and the surfaces will dimple, wrinkling. This is the type of ikura that is cheaper and often served at the cheap conveyor belt sushi restaurants.

The most commonly used roe in conveyor belt sushi restaurants is ikura from cheap Alaskan or Russian Chum salmon. An even cheaper type is masuko. Besides the masu roe, raw materials included soy sauce, salt, fermented seasoning, amino acids, reduced sugar syrup, enzymes, fish sauce, and fish and shellfish extract. For homemade versions, only soy sauce, mirin (sweet cooking sake) and sake are used.

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What is Salmon caviar?

In Japan, salmon roe that has been separated from the ovarian membrane and then salted is called ikura. At sushi restaurants, this is also marinated in broth that includes soy sauce, mirin and sake. This is called ikura marinated in soy sauce, or simply ikura. Worldwide, caviar is considered to be of more value than ikura. Therefore, in an attempt to improve the impression of soy sauce-marinated ikura, it is sometimes called ‘salmon caviar’. This is behavior especially seen among manufacturers selling soy sauce-marinated ikura.

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Revision date: March 9, 2021

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What is Red caviar?

Not to belabor the point, but the following is dependent on the following. In Japanese salmon is referred to as “鮭” (sake/salmon) or “鱒” (masu/trout). The characters look different, but they are part of the same family and there aren’t clear biological categories to separate them into. Incidentally, in English the type that makes their way into the sea are called “salmon,” and those that remain in freshwater their entire lives are known as, “trout.” They are all considered to be part of the salmon family. Now, foreigners who know about Japan may imagine Japanese sake (the alcoholic beverage) when they hear the word “sake” so we spell sake/salmon as “shake”, which is close to the sound pronounced by Japanese people.

First of all, shake is mainly Chum salmon, caught in the seas near Japan. Masu caught in the seas near Japan are mostly Pink salmon (Humpback salmon) and Sakura masu. Masu caught in rivers and lakes are generally Char or Rainbow trout.

Now we finally get to the topic of this article, shake roe that has been removed from the ovarian membrane then salted or marinated in soy sauce is called ikura while masu roe is called masuko and they are clearly distinguished. This is because masuko can be bought at just 20-40% of the cost of ikura. However, the difference is really that each egg is smaller than that of ikura and in general people can’t taste a difference.

Over the past 10 years or so, the masuko made from the roe of Rainbow trout farmed in France and the masu farmed in Japan have been called ‘red caviar’ by manufacturers. Of course black caviar made from the roe of sturgeon and tobiko made from the roe of flying fish are distinctive. Certainly there is no problem in calling fish roe caviar according to the Product Labeling laws, but it’s extremely clear that they are only trying to get a higher price out of it.

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Revision date: March 9, 2021

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What is ken?

Ken (剣) is a traditional Japanese garnish made from finely shredded vegetables like daikon radish. It is often seen alongside sashimi. While commonly mistaken for tsuma, ken has its own distinct role in Japanese plating and presentation.

It is not merely decorative—it helps absorb moisture, maintains freshness, and enhances the visual balance of the dish.

Ken is considered to be better the longer and thinner it is, but this is a mistake. Not only is Ken tangled and difficult to eat, but it also doesn’t give any sense of the flavor of the materials. It’s long been said that 10 cm is a reasonable length and this is also the length that looks the most refined. Creating ken requires precise knife skills, and its neatness often reflects the chef’s craftsmanship.

Many people believe that the thinly cut daikon radish strips that accompany sushi are tsuma. That is not tsuma. It’s called ken. Besides daikon radish, udo, pumpkin, cucumber, carrots and turnips are also used. It is cut into thin strands and stood up next to sashimi like a sword (which is called “ken” in Japanese). However, when the sashimi is laid on top of it, it is called shikitsuma. While it is a bit confusing, in that case it is a type of tsuma. The simplicity and elegance of ken align with the Japanese aesthetic of minimalism and natural beauty.

Since the Meiji era, combos of many different types of sushi have become popular, and with it larger dishes have become necessary. Therefore, there has also been a tendency to make it more showy. It’s only natural that the types of tsuma increase to place focus on the highly valued seafood, but if there is too much ken, it will take over the space meant for the sashimi.

What is Tsuma?

In Japanese cuisine, “Tsuma” refers to ingredients that are added to sashimi, soup dishes, and other dishes to enhance their color and flavor. Many people think that the shredded daikon radish served with sashimi is “Tsuma.” However, this is actually called “Ashirai,” and depending on how it is cut and where it is placed, it is classified into three types: “Tsuma,” “Ken,” and “Yakumi.”

More specifically, Tsuma itself can also be categorized into three types.

One is Shikitsuma (pronounced ‘shikizuma’ in Japanese) which consists of things like green shiso and cucumber leaves that sashimi is laid on. Another is Metsuma (pronounced ‘mezuma’ in Japanese) which is made from aome and murame. The final is Tatetsuma (pronounced ‘tatezuma’ in Japanese) used to prop sashimi up like hanahojiso and hanamaru kyuri (花丸胡瓜又は花付き胡瓜). All Tsuma is served to bring out the charm of sashimi.

One point of note is that the most commonly used shikitsuma, green shiso, is occasionally used to obstruct fragrances that are too strong for white fish and shellfish like flatfish and flounder. Furthermore, it’s a rule that shikitsuma, which is a leaf, is not used on plates shaped like a leaf, but what is served and how it is arranged is ultimately up to the chef.

In the end, Tsuma is not merely a garnish—it is an integral part of Japanese culinary aesthetics, harmonizing taste, seasonality, and visual beauty.

Image of Metsuma: Aome (Here, ao refers to green) is on the left and murame (Mura means purple) is on the right in the image.

Image of Hanahojiso (花穂紫蘇): It is the spike of perilla with flowers about to bloom.

What is Toro salmon?

You probably already know this, but “toro tuna” is not the name of a type of fish. “Toro” is the name of a fatty part of the tuna. The fat content and attributes of the belly side of the tuna are completely different from that of the dorsal side. Toro is the name of the part near the head, mostly on the belly side.

In the same way, there is no fish called “toro salmon”. Just like tuna, “toro” refers to the fatty part on the belly side of the salmon. It is also called “harasu” in Japanese. This is how the word is used at some scrupulous sushi restaurants. This description of “toro salmon” is correct.

Most salmon used at conveyor belt sushi restaurants is either trout salmon or Atlantic salmon. The reason this salmon can be served at the cheap price of US $1 or $2 per plate (2 pieces of sushi) is that these particular fish are all farmed and are available in bulk quantities from overseas. This salmon is mainly imported to Japan from Norway, Chile, Scotland and Canada.

Actually, the popular “toro salmon” topping is made from these imported items and the fat content is three times that of wild salmon. Feeding farmed salmon plenty of solid compounded feed that is high in protein and high in fat, turns the entire body to toro.

Salmon, which are born in freshwater and migrate downstream to the sea are called “sea-run fish” and they may be farmed in either seawater or freshwater. Trout salmon is “former” rainbow trout that was raised in a fish cage in the sea. In the wild, the sea-run rainbow trout grows up to 1 m in length, its body turns silver and the meat takes on a red color. The wild version of these are called “steelhead” and fetch a high market price, so they are not used in conveyor belt sushi restaurants.

Just like other aquaculture, salmon farming faces some difficult issues. It may surprise you that salmon is actually a white fish, originally. In the wild, the salmon meat gets a red color from feeding on crustaceans such as crab and shrimp that contain the red pigment astaxanthin. However, in the fish cages where the salmon are surrounded by nets, the food chain is also restricted. The compound feed would be plenty if the goal was only to raise bigger fish, but that results in a grey color or light yellow meat that doesn’t even resemble the salmon pink (orange?) that everyone wants and they don’t sell.

Therefore, when making the solid compounded feed, artificial coloring is mixed in. One of the colorings is called canthaxanthin. This is a synthetic chemical derived from petroleum. There is a color chart with 10 different, detailed levels of red coloring and buyers can even indicate which color they would like and the farmers can achieve it. It’s kind of like an industrial product that is being manufactured. Japanese people prefer a dark red color for salmon in the same way they do for tuna, so the coloring for Japan’s market is adapted to that.

When light is shone on wild salmon, the red coloring looks faded, but the light makes farmed salmon that have been fed coloring, look brighter. Artificial coloring is a necessity in farmed salmon and this is true for the trout salmon and Atlantic salmon that are used as the ingredients for toro salmon as well. All of the farmed salmon in circulation have been colored in this way, so much so that it wouldn’t be surprising if the insides of their stomachs were stained red. The flamingos at zoos also get their beautiful pink feathers from these chemicals.

Trout salmon is rainbow trout that has been farmed in the sea. On the other hand, rainbow trout farmed in freshwater is called Donaldson trout. Of all the large rainbow trout gathered at each location, those with small heads and fat bodies were selected and bred over many years to create this type. The objective of choosing a small head is to make more meat. They are characterized by their fast growth and while normal, farmed rainbow trout grow to about 30 to 40 cm, Donaldson trout grow up to nearly 1 m. The name is taken from the American who developed this variant.

The Donaldson trout is farmed throughout Japan and is used as toro salmon and aburi salmon at conveyor belt sushi restaurants. Since they are supplied directly to the processor (of the salmon) from the farmer without going through the market, they may be sold cheaper than the import price. Just like the imported salmon, this farmed salmon is also fed artificial coloring. There are also already new variants improved from the Donaldson trout being bred. Trout made from breeding Donaldson trout females and steelhead males are called Donaldson steelhead, for instance. They grow even faster.

Ample use of the latest biotechnology has been made in salmon farming and some of these technologies include creating young fish without functioning reproductive organs, “triploids” which means increasing the size of the fish up to triple and “all female populations” where males are converted into females. The triploid fish grow large in correlation to the lack of energy exertion. The objective of all-female populations is to get more masuko (ovaries). Masuko is used for the ikura (salmon roe) at conveyor belt sushi, and since the fish that the roe is harvested from have an inferior flavor, they are used for aburi salmon. Now, there are even triploid, all-female farm populations. No wonder the restaurants can serve a plate (2 pieces) of salmon sushi for US $1.

The simple phrase, “toro salmon” contains so much meaning.

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