Blackmouth splitfin (Sumikuiuo)

Blackmouth splitfin (Sumikuiuo) is widely distributed along the Pacific coast from Hokkaido to the southern coast of Kyushu, along the Sea of Japan coast from Hyogo Prefecture to the northwestern coast of Kyushu, the East China Sea, southern Taiwan, the Pacific Ocean, and the Indian Ocean. It inhabits continental shelves and slopes of seamounts at depths of 50 to 1,000 meters (most commonly 100 to 800 meters). The body is slender and laterally compressed. Its body color is blackish brown, with a lighter color on the ventral side. Most individuals are about 30 cm in length.

The name “Sumikuiuo” seems to derive from the black color of the rear part of the mouth. It is caught using bottom trawl nets and used as an ingredient in processed products. In many cases, it was discarded from the boat immediately after being caught.

In Minamisatsuma City, Kagoshima Prefecture, which serves as a base for deep-sea trawl fishing, there is a collaborative initiative called the “Kagoshima Deep-Sea Fish Research Society,” involving academia, industry, and government, in cooperation with the Fisheries Department of Kagoshima University and a fisheries wholesaler. This group is engaged in promotional activities to promote the utilization of deep-sea fish.

Through the activities of this research society, including businesses and restaurants, deep-sea fish are now served and sold in many establishments across Kagoshima Prefecture. Sumikuiuo is also enjoyed in various dishes, such as sashimi.

Interestingly, Sumikuiuo was once classified as the same species as Nodoguro, which suggests it is a fatty and flavorful fish. Recently, it has begun to be served at sushi restaurants in Tokyo, and its deliciousness is gaining recognition.