Flatfish in Basel Zoo, Switzerland

Flatfish are easy to identify. In an adult flatfish, both eyes are on the dark (pigmented) side of the body, while the other side is eyeless and white. Flatfish lie on the bottom with the dark side up and the pale side down. Flatfish can change color to camouflage themselves to match the bottom. Their shape and color makes it easy for them to lie on the bottom and hide from both predators and prey. Most flatfish swim close to the bottom by undulating their bodies. They have long dorsal and anal fins to help them move along the bottom. Flatfish do not start out life flat. The larvae look like most other fish. They are the same color on both sides, and have one eye on each side of the head. As the flatfish grow, their color and pigmentation patterns change and one eye migrates across the top of their heads to end up on the same side as the other eye.