Aburasokomutsu Sushi
A Comprehensive Overview of Escolar in Japanese Sushi Cuisine

Aburasokomutsu 油底鯥(アブラソコマツ) 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 sushi display (neta bako) 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). 

As the flesh of the aburasokomutsu 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.^[1]

Wrong marking, whether due to ignorance or deception, is a serious problem, especially with the escolar. Aburasokomutsu can cause digestive disorders, especially diarrhea respectively 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 as a source of risk for natural poisoning from abnormal lipids and has banned its sale for consumption since 1981.^[2]

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 escolar.^[3]

The 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 (6.56 ft) and weigh up to 45 kg (ca. 99 lb). Juveniles in particular, but also larger individuals, migrate vertically to the surface at night to feed on fish, crustaceans and especially squid.

The economy of aburasokomutsu, known as Lepidocybium flavobrunneum, is influenced by various factors, including its economic value, ecological impact, and challenges related to identification and management. L. flavobrunneum is occasionally misidentified and mislabeled in the seafood supply chain, undermining consumer confidence and disrupting economic transactions.^[4] Additionally, it is sometimes used to adulterate high-value seafood products, leading to economic losses and potential health risks for consumers.^[5] Despite its relatively low economic value as bycatch in some fisheries ^[6], such as the U.S. pelagic longline fishery, understanding its catch per unit effort (CPUE) and biological characteristics is crucial for sustainable management-^[6][7]

In summary, the economy of Lepidocybium flavobrunneum is small but complex. It is influenced by factors such as mislabeling, illegal fishing, and the economic viability of fisheries. Sustainable management practices based on integrated ecological-economic models and effective measures to combat illegal fishing are crucial to ensuring the long-term economic and ecological sustainability of escolar fisheries.