Flounder, any of several flatfish having both eyes on one side of the body. This exposed side, as the fish lie on their side on the ocean bottom, is the left side in one family of flounders and, almost always, the right side in the other family. The body is flat, with scales present in some species and absent in others; the body is colored only on the exposed side. The families include such fishes as the halibut, turbot, and dab. All flounders are valued as food fishes. Several of the common species are called flukes.

In the United States the most important species of flounder is the summer flounder, also called plaice and deep-sea flounder, which is found in the Atlantic Ocean from Massachusetts to Florida. The adult summer flounder may grow to a length of about 1 m (about 3 ft) and a weight of about 7 kg (about 15 lb). It feeds on small marine animals, such as shrimp, crab, and small fish. Large quantities of these fish are captured between May and October. The winter flounder, or lemon sole, and the fourspot flounder are found along the South Atlantic coast and in the Gulf of Mexico. The diamond turbot, found along the Pacific coast, is another common species. The plaice of western Europe grows to 60 cm (24 in) and 4.5 kg (10 lb). Two species of flounder are found along the coasts of Great Britain. Several other species are found in Arctic waters.

Scientific classification: Flounders constitute the families Bothidae and Pleuronectidae. The summer flounder is classified as Paralichthys dentatus. The winter flounder is classified as Pseudopleuronectes americanus. The fourspot flounder is classified as Paralichthys oblongus, the diamond turbot as Hypsopsetta guttulata, and the plaice as Pleuronectes platessa.
 

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