Flatfish

A flatfish is a member of the ray-finned demersal fish superorder Pleuronectoidei, also called the Heterosomata. In many species, both eyes lie on one side of the head, one or the other migrating through or around the head during development. Some species face their left sides upward, some face their right sides upward, and others face either side upward. The most primitive members of the group, the threadfins, do not resemble the flatfish but are their closest relatives. Many important food fish are in this order, including the flounders, soles, turbot, plaice, and halibut. Some flatfish can camouflage themselves on the ocean floor.

Source: Wikipedia