Opium fish only eat the head, because the opium fish is an imported fish, the head is cheaper than the whole fish, and the body is usually processed into a variety of food, such as fish fillets. Most of China's "opium fish heads" come from Russia, while a small portion is farmed.

Opium fish is a member of the family of plaice, a family of bony fishes called plaice, which belongs to the flounder family. Most of the opilio grows in the cold water area of the outer sea, living in a particular area of the sea all year round, and does not have the habit of long-distance migration.