In Japanese, aka means “red,” shiro means “white,” kuro means “black,” and gin means “silver.” Accordingly, names such as Akamutsu, Shiromutsu, Kuromutsu, and Ginmutsu can be understood as combinations of color terms with the fish name Mutsu.
Before examining each fish individually, it is useful to consider the meaning of the term Mutsu itself.
In certain dialects of the Shikoku and Chugoku regions, the expressions mutukoi or mutukkoi describe food that is “rich,” “heavy,” or “greasy,” as opposed to light and refreshing. This descriptive term, which emphasizes richness in fat, is thought to have evolved into the fish name Mutsu. In other words, the word Mutsu in fish names signifies “a fish rich in fat.” This designation was then combined with visible characteristics, such as coloration, to yield names like Akamutsu and Kuromutsu.
With this background in mind, let us now examine the four types of Mutsu, along with some related species.
Akamutsu (Common Name: Nodoguro)
The official name is Akamutsu, though it is more widely recognized by the common name Nodoguro (“black throat”), referring to the distinctive dark coloration at the back of its throat. Taxonomically, it belongs to the family Acropomatidae and is not closely related to the Kuromutsu of the family Scombropidae, discussed later.
Akamutsu is distributed primarily in western Japan and southward, as well as along the Sea of Japan coast. Kuromutsu, by contrast, inhabits the Pacific Ocean south of Iwate Prefecture and the Izu Islands. Compared to Kuromutsu, Akamutsu tends to live in slightly shallower waters.
Shiromutsu (Official Name: Oomehata)
Shiromutsu is a colloquial name; its official designation is Oomehata. Like Akamutsu, it does not belong to the family Scombropidae. It came to be called Shiromutsu because its flesh is whitish and rich in fat. Its formal name, Oomehata (“big-eyed grouper”), reflects its strikingly large eyes and a mistaken assumption of close relation to the grouper family.
In the Kanto region, the name Shiromutsu is more commonly used, though it is also sometimes referred to as Ginmutsu, leading to confusion. While it resembles Akamutsu in appearance, it can be distinguished by its very large eyes and a triangular anal fin.
Kuromutsu
The catch volume of Kuromutsu is quite limited, making it rare in ordinary household cuisine. Like Akamutsu, it has exceptional fat content and is considered among the most flavorful of fish. Due to both its rarity and its taste, it commands premium prices, sometimes surpassing even renowned high-end species such as Kue or Akamutsu.
Ginmutsu (Marketed Today as Mero)
Ginmutsu is the former Japanese market name for the Majeranainame (Common name is Patagonian toothfish), a large deep-sea species inhabiting waters around the Antarctic. A white-fleshed fish with a high fat content, it was once distributed in Japan as “Ginmutsu.” However, because it is taxonomically unrelated to Akamutsu and Kuromutsu, the use of this name was prohibited after the 2003 revision of the JAS Law, in order to prevent consumer confusion. Today, it is typically marketed in Japan under the name Mero.
Baramutsu and Aburasokomutsu (Related Species)
As a brief digression, Baramutsu and Aburasokomutsu are also fish whose names contain mutsu. Baramutsu is a deep-sea species in the family Gempylidae, characterized by an extremely high lipid content. Its flesh contains large amounts of wax esters, a type of indigestible oil, which can cause stomach pain and diarrhea in humans. For this reason, distribution of Baramutsu is prohibited in Japan.
Nevertheless, it is sold in the United States and is sometimes used deceptively as a substitute for other fish, although it is said to have an exquisite taste. In any case, members of the blackfin scabbardfish family, including Aburasokomutsu and Baramutsu, must be approached with caution due to their potential adverse health effects when consumed.
Mutsu (Standard Japanese Name)
The standard Japanese name Mutsu refers to a fish of the family Scombropidae. It closely resembles the Kuromutsu and is similarly prized for its rich, fatty flavor. This deep-sea fish is landed across Japan, from Hokkaido to Kyushu, and has long been regarded as a premium fish, especially in the Kanto region, where it is traditionally used in simmered dishes.
Because of their similar body shape and coloration, Mutsu and Kuromutsu are often not clearly distinguished and both may be sold as Kuromutsu. In the marketplace, however, they differ in price: Kuromutsu typically sells for more than twice the price of Mutsu, making cost an effective indicator of distinction.
Availability in Sushi Restaurants
In Tokyo sushi restaurants, the varieties most commonly offered are Akamutsu, Mutsu, and Kuromutsu. Since Mutsu and Kuromutsu are easily confused, many establishments label them uniformly as Kuromutsu. All of these are regarded as luxury fish, served only in select high-end sushi restaurants.
In my view, these toppings reach their full potential only when paired with shari seasoned with rich red vinegar and served with precise temperature control. Many sushi restaurants use lighter rice vinegar, which does not always harmonize with the oiliness of these fish. In some cases, it may even be necessary to prepare two different kinds of rice. Furthermore, in Tokyo, a single piece of such nigiri typically costs upwards of US$20.
Related contents:
Blackthroat seaperch (Akamutsu)
Silvergray seaperch (Oomehata)
Silverbelly seaperch (Wakiyahata)