Flatfishes: Pleuronectiformes

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FLATFISHES: Pleuronectiformes



Flatfishes have both eyes on the same side of the head. The body is disk-shaped or oval. These fishes are 1 inch (2.5 centimeters) to 6 feet, 6 inches (2 meters) long and weigh as much as 661 pounds (300 kilograms), but most are about 12 inches (30 centimeters) long. The eye side of most flatfishes is dark brown or black, sometimes with spots, bands, or wavy stripes. The other side is usually white or pale yellow. The dorsal (DOOR-suhl) fin, the one along the center of the back, extends from just above the eyes to the tail. The anal fin, the one along the midline of the belly, also is quite long. Adult flatfishes do not have a swim bladder, an internal sac that fishes use to control their position in the water.


Flatfishes live all over the world.


Most flatfishes live in coastal waters over sand and mud bottoms.


Flatfishes eat invertebrates (in-VER-teh-brehts), or animals without backbones, and fishes.


Except for halibuts, which chase other animals for food, flatfishes lie on the bottom and ambush their prey, or animals killed for food. When flatfishes swim, they glide with wavy movements. Most flatfishes are active during the day, some around sunrise and sunset, and others at night. Flatfishes do not form schools.

Some flatfishes travel great distances to spawn once a year. Males of some species become aggressive toward one another during the mating season. Males and females probably pair up for spawning, or release of eggs. The eggs are fertilized (FUR-teh-lyzed), or joined with sperm, outside the female and drift in the water. When they hatch, flatfish larvae (LAR-vee), or the early stage that must change form before becoming adults, drift freely. After their eyes move to one side of their head, flatfishes live on the bottom.


Flatfishes are important food fishes.


All flatfishes begin life with one eye on each side of the head. During the change from larvae to adults, one eye moves from one side of the head to the other, so that both eyes end up on the same side. Depending on the species, either the right or the left eye migrates. The eyes may be close together or far apart when the eye travel is completed.


The World Conservation Union (IUCN) lists one species of flatfishes as Endangered and one as Vulnerable. Endangered means facing a very high risk of extinction in the wild. Vulnerable means facing a high risk of extinction in the wild.


Physical characteristics: The eyes of peacock flounders are on the left side of the head. There is a wide space between the eyes, and the lower eye is farther forward than the upper eye. Males have a strong spine on their snout. The body is disk-shaped. The eye side of the body is grayish brown with many bright blue rings and two or three large black spots. Peacock flounders can grow to a length of about 18 inches (45 centimeters) but usually are about 14 inches (35 centimeters) long.

Geographic range: Peacock flounders live in the western part of the Atlantic Ocean from Bermuda to Brazil.

Habitat: Peacock flounders live in shallow water near the shore on sandy bottoms, on coral reefs, among sea grass, and in mangrove forests.

Diet: Peacock flounders eat small fishes, crustaceans, and octopuses. Crustaceans (krus-TAY-shuns) are water-dwelling animals that have jointed legs and a hard shell but no backbone.

Behavior and reproduction: Peacock flounder are active during the day. They rest on the sandy bottom, waiting in ambush for their prey. When swimming, these fish glide just above the bottom using wavy movements. Peacock flounder can change colors rapidly to blend in with their background. To begin mating, male and female peacock flounders approach each other with pectoral fins held up. The pectoral (PECK-ter-uhl) fins correspond to the front legs of four-footed animals. The male then positions himself under the female, and the pair slowly rises off the bottom. The fish then release eggs and sperm at the same time and rapidly return to the bottom.

Peacock flounders and people: Peacock flounders are caught by accident by people trying to catch other fish.

Conservation status: Peacock flounders are not threatened or endangered. ∎


Physical characteristics: Female Pacific halibut reach a length of almost 9 feet (2.7 meters) and a weight of about 498 pounds (226 kilograms). Males are about half that size. The eyes of Pacific halibut are on the right side of the head, and the upper eye is farther forward than the bottom eye. The body is thick and diamond-shaped. The eye side is greenish brown to dark brown or black with lighter blotches. The other side usually is white, sometimes with blotches.

Geographic range: Pacific halibut live in the northern part of the Pacific Ocean.

Habitat: Pacific halibut live near the shore on a variety of bottom types.

Diet: Small Pacific halibut eat bottom-dwelling invertebrates and small fishes. Larger halibut eat almost anything they can catch.

Behavior and reproduction: Pacific halibut are active during the day. They often rise off the bottom and may come close to the surface when chasing prey. Pacific halibut spawn in deep water, move to shallower water for the summer, and then return to deep water. Females can reproduce when they are about twelve years old and males when they are about eight years old. The eggs are fertilized outside the female. Pacific halibut live about forty years.

Pacific halibut and people: Pacific halibut is an important food fish.

Conservation status: Pacific halibut are not threatened or endangered. ∎


Physical characteristics: The eyes of common sole are on the right side of the head. The body is long and thick. On the eyeless side, the head and snout are covered with white bumps. The eye side is dark brown or grayish brown with darker blotches. The eyeless side is creamy white. The dorsal and anal fins are edged in white, and the pectoral fin on the eye side has an oval black patch. These fish reach a length of about 28 inches (70 centimeters) and a weight of about 6 pounds (3 kilograms), but most are 12 to 16 inches (30 to 40 centimeters) long.

Geographic range: Common sole live in the Atlantic Ocean from Norway to Senegal.

Habitat: Common sole live on soft sandy or muddy bottoms.

Diet: Common sole eat small, bottom-dwelling invertebrates, but sometimes they eat small fishes.

Behavior and reproduction: Common sole are bottom dwellers that live alone. They spend the day partially buried or lying on the bottom. At night they sometimes move off the bottom. Common sole can reproduce when they are three to five years old. Spawning grounds are in both shallow and deep waters. The eggs float in open water. Common sole live seven to eight years.

Common sole and people: Common sole is an important food fish.

Conservation status: Common sole are not threatened or endangered. ∎



Gilbert, Carter Rowell, and James D. Williams. National Audubon Society Field Guide to Fishes: North America. New York: Knopf, 2002.

Schultz, Ken. Ken Schultz's Field Guide to Saltwater Fish. New York: Wiley, 2004.

Web sites:

"The Flounders and Soles." Fishes of the Gulf of Maine. http://www.gma.org/fogm/flounders_soles.htm (accessed on November 9, 2004).

"Halibut." Seafood Choices Alliance. http://www.seafoodchoices.com/seasense/halibut.shtml (accessed on November 9, 2004).

Jamal, Rina Abdul. "Eye Travel." AnimalFact.com. http://www.animalfact.com/article1012.htm (accessed on November 8, 2004).