Flounder, the common name of some species of saltwater flatfish. Like other flatfish, the adult flounder has both eyes on one side of its head, and it swims and rests with this side of its body up. Flounders are bottom-dwellers, and feed on other fish, shrimp, crabs, and worms. They are found in almost all seas.

The summer flounder (or fluke) and the winter flounder (or blackback flounder) are important food fishes. The summer flounder ranges from Maine to Florida. Some individuals grow up to 3 feet (90 cm) long and weigh about 15 pounds (6.8 kg). The winter flounder, found from Labrador to Georgia, rarely exceeds 15 inches (38 cm) in length and 4 pounds (1.8 kg) in weight. The peacock flounder, which has blue markings, ranges from Bermuda to Brazil. It grows to a length of 18 inches (45 cm). An important sport fish is the starry flounder, which is found from Alaska to southern California.

The winter flounderThe winter flounder rarely exceeds fifteen inches in length and four pounds in weight.
Why Does a Flounder Change Colors?

A flounder changes color to hide from enemies and to surprise its prey. A flounder lives at the bottom of the sea. Lying flat on its side, a flounder can change its color and pattern to match the sea floor. For example, if a flounder is lying on a sandy area, its markings begin to look like grains of sand.

After a flounder settles on the ocean floor, it wiggles its fins. The motion stirs up sand and shells. The sand and shells settle on the edges of the flounder’s body. That makes the flounder even harder to see.

When it hatches, a flounder looks about the same as a small salmon. As it grows, its body becomes thin and flat. One eye moves to the other side of the head. This helps a flounder see better when lying on the ocean floor.

The summer flounder is Paralichthys dentatus; the peacock flounder, Bothus lumatus. Both are of the family Bothidae. The winter flounder is Pseudopleuronectes americanus; the starry flounder, Platichthys stellatus. Both are of the family Pleuronectidae.