Flat Fishes

Flat Fishes (Pleuronectidee), an important family of Anacanthinous food-fishes with thirty-four genera and about 200 species from all seas except those of the highest latitudes. They are most numerous in the tropics, but the largest species are from the temperate zone. The young are symmetrical with the eyes in the normal position, and swim vertically in the open sea. The adult forms are ground fishes, markedly unsymmetrical, having the body greatly compressed from side to side, with the eyes on the upper surface, which may be the right or left, and swimming horizontally with an undulating motion. How the change in the position of the eyes is effected is uncertain. The colour of the upper side assimilates with the ground on which they lie concealed; the under surface is generally colourless. The dorsal and anal fin usually extend the whole length of the body without division. The type-genus Plenronectes, from the north temperate zone, has 23 species. The most important British flat-fishes are the brill, dab, flounder, plaice, sole, and turbot (all which see).