[flat-fish] 
) -fish, (especially referring to two or more kinds or species) -fish⋅es. | any fish of the order Heterosomata (Pleuronectiformes), including the halibut, sole, flounder, etc., having a greatly compressed body and swimming on one side, with both eyes on the upper side in the adult. |
| flat·fish (flāt'fĭsh') n. pl. flatfish or flat·fish·es Any of numerous chiefly marine fishes of the order Pleuronectiformes, including the flounders, soles, and halibuts, having a laterally compressed body with both eyes on the upper side. |
flatfish
any member of the order Pleuronectiformes, which includes about 600 species of bony, oval-shaped, flattened fishes such as the flounder, halibut, and turbot. The pleuronectiforms are unique among fishes in being asymmetrical. They are strongly compressed, with both eyes on one side, while other fishes and vertebrates in general are bilaterally symmetrical. The asymmetry is believed to have evolved from a generalized, symmetrical percoid (sea bass) body pattern in a fish that habitually rested on its side. Larval flatfishes have an eye on each side of the head, but during a period of rapid body change (metamorphosis) one eye migrates to the other side of the head, after which the larvae settle to the bottom. Osteological changes resulting from the eye migration are responsible for the asymmetry in the flatfish skull.
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