Olive Flounder

The olive flounder is a large left-eyed flatfish in the family Paralichthyidae, native to the coastal waters of East Asia, including Japan, Korea, and China. It is also known as Japanese flounder and, in some regional English usage, bastard halibut. The species is demersal, living on sandy seafloor in coastal and estuarine waters, and is one of the most economically significant flatfish in East Asian aquaculture and fisheries. Olive flounder are relatively large for coastal flatfish, with a broad, muscular body and a large mouth adapted for capturing active prey such as small fish. The species has also been introduced or farmed outside its native range in some aquaculture operations.

• Broad, oval, muscular body typical of large predatory flatfish
• Eyes on the left side of the head
• Upper side is olive-brown to dark brown with numerous small dark and light spots, sometimes with scattered white blotches
• Large mouth with well-developed teeth, extending past the eye
• Underside is white, occasionally with dark blotches in older individuals
• Adults commonly reach 40-70 cm, with large individuals approaching 1 m

The large mouth and sharp teeth distinguish it from smaller, small-mouthed soles found in the same region, while its olive-brown mottled pattern helps separate it from paler, plainer local flatfish species.

Olive flounder are found along the coasts of Japan, the Korean Peninsula, and China, including the Yellow Sea, East China Sea, and adjacent waters. They inhabit sandy or sand-mud seafloor in coastal, estuarine, and nearshore waters, typically from very shallow depths down to around 100-200 meters. Juveniles often use shallow, sheltered coastal areas and estuaries as nursery habitat before moving to slightly deeper offshore waters as they mature. The species tolerates a range of temperate coastal conditions across its native range.

Olive flounder are active, ambush-style predators that partially bury themselves in sand and lie in wait for passing prey, primarily small fish, shrimp, and crabs. They are capable of short bursts of swimming to strike at prey or evade predators. The species undergoes the typical flatfish larval stage, with pelagic eggs and larvae developing symmetrically before undergoing eye migration and settling to the seafloor as juveniles. Olive flounder are among the most heavily farmed marine flatfish species in East Asia, with extensive aquaculture operations supporting regional fisheries alongside wild populations.