Aburasokomutsu Sushi

Aburasokomutsu is the Japanese name for the escolar, which is sometimes referred to “butterfish” or incorrectly “white tuna”. Although occasionally referred to as a butterfish, the Escolar is not a member of the butterfish family, but a member of the snake mackerel family. Unlike in Japan, you can often find aburasokomutsu in the display (neta-bako, ネタ箱) of western sushi bars and restaurants.

The name “butterfish” or “white tuna” originates from a purely commercial motivation and should sound more appealing to the consumer. However, its full-bodied, very fatty and slightly sweet taste, reminiscent of butter, cannot be denied.

There is hardly any other fish that is better suited to the false name “butterfish” or “white toro” than the escolar. The shiny, matte white meat is firm, very tender, full-bodied and accompanied by aromas that have a strikingly strong taste of butter. Compared to tuna, the meat is slightly more sour and less fresh in taste.

When preparing as Sushi or Sashimi, one should avoid the excessive use of soy sauce or wasabi, a thin glaze is more sufficient. Alternatively, the buttery flavors harmonize very well with a touch of citrus (e.g. yuzu, 柚子).

As the flesh of the escolar contains wax-like lipids, one should refrain from eating larger quantities, as these cause digestive problems (keriorrhea).

Investigations by the marine protection organization Oceana, showed that escolar was wrongly labeled both in restaurants and at fish markets. The Oceana study concluded that from 2010 to 2013, approximately 84 percent of the 114 tuna samples identified as "white tuna" were actually escolar [Warner et al., 2013].

Wrong marking, whether due to ignorance or deception, is a serious problem especially with the escolar. Aburasokomutsu (escolar) can cause digestive disorders, especially diarrhea (lat. keriorrhea), when consumed due to the wax-like lipids contained in the meat. These lipids are heat-resistant and do not disintegrate when heated. In the absence of specific dose-response studies in the medical literature, doses as low as 95 grams are estimated to be laxative.

The Japanese Ministry of Health, Labor and Welfare (厚生労働省) lists aburasokomutsu (escolar) as a source of risk for natural poisoning from abnormal lipids and has banned its sale for consumption since 1981 [MHLW, 2020].

In June 1998, a publicized food poisoning occurred in Tokyo due to the consumption of cooked fish on the lunch menu of a restaurant. Twenty-one out of forty people were poisoned. Their main symptoms were skin irritation, headaches and palpitations. The subsequent convened official investigation confirmed that the prepared fish responsible for the poisoning was aburasokomutsu (escolar) [Kan et al., 2000].

The aburasokomutsu (escolar) prefers temperate and tropical waters, especially on continental slopes, around the world. They are usually found individually or in pairs, usually at a depth of 200-1100 m (656-3609 ft). Adult specimens can reach a size of over 2 m (6.6 ft) and weigh up to 45 kg (99 lb). Juveniles in particular, but also larger individuals migrate vertically to the surface at night to feed on fish, crustaceans and especially squid.

According to the Food and Agriculture Organization of the United Nations (FAO), the three largest fishing nations in 2018 were Ecuador, Spain and Portugal. Aburasokomutsu (escolar) is rarely targeted and is often part of the by-catch of other species [Levesque, 2010].

Distribution Area of Aburasokomutsu

1. GEMPYLID: Consumption, especially of larger quantities, can cause digestive problems (keriorrhea). Keriorrhea is the production of greasy, orange-colored stool, which is caused by the consumption of indigestible wax esters. Persons with stomach or intestinal irritation should avoid consumption. [FDA, 2021]
2. SCOMBROTOXIN: The naturally have high levels of enzymes causes the meat to let it rot quickly. It is therefore essential to maintain an appropriate cold chain until prompt processing. Histamine is not destroyed by normal cooking temperatures, so even properly cooked fish can still result in poisoning. [FDA, 2021]