Flatfish, also known as sole, is a general term for fishes of the order Haliotis. The body is very flat, oblong, oval or long tongue-shaped, and the maximum length can reach 5 m. The adult fish body is asymmetrical left and right. Both eyes are located on the left or right side of the head. The mouth is slightly prominent. Fins are generally spineless. The dorsal fin and the anal fin are long in base, connected or not connected with the caudal fin. Widely distributed in warm and hot seas of various oceans, it mainly feeds on benthic invertebrates and fish. There are more than 540 species in the world, including 120 species made in China. The main species are Siniperca chuatsi, Siniperca flounder, sole and tongue sole, which are economic fish. Habitat in the sandy bottom of shallow sea, preying on small fish and shrimp. They are especially suitable for benthic life on the seabed. Because their bodies are flat. Both eyes are on the upward side of the body, and the color of this side is well matched with the surrounding environment; Their downward side is white. The flounder has extremely fine scales on its body surface. The flounder has only one dorsal fin, which extends almost from the head to the caudal fin. They mainly live in temperate waters and are important economic fish in temperate waters.