Flounder (Platichthys flesus)

FishFlatfishCamouflage

Overview

Flounders are flatfish (order Pleuronectiformes) — bottom-dwelling fish with one of the strangest body plans in the animal kingdom. As an adult, a flounder lies flat on the seabed on one side of its body, with both eyes on the upper side and a pale, blind underside. The European flounder (Platichthys flesus), shown here, is a typical example, with a flat, oval, mottled body that blends into sand and mud.

The truly remarkable part is how it gets that way: a flounder begins life as an ordinary, symmetrical larva with one eye on each side, and as it grows, one eye gradually migrates across the head to join the other — a dramatic transformation few other animals undergo.

Note: “flounder” covers several flatfish species; details here use the European flounder as a reference. Treat general statements as approximate and verify against authoritative sources.

Habitat & Range

Flounders live on soft seabeds — sand, mud, and gravel — in coastal seas, estuaries, and bays, and several species (including the European flounder) move into brackish and even fresh water. They favour shallow waters where they can lie camouflaged on the bottom, and they are found across many temperate and tropical coasts depending on the species.

Diet

Flounders are carnivores that ambush prey from the seabed. They eat worms, crustaceans, molluscs, and small fish, lying hidden and snapping up prey that comes within reach, or rooting through the sediment for buried invertebrates. Their upturned eyes let them watch for both food and danger while the rest of the body stays concealed.

Behavior

Camouflage is central to a flounder's life: it can change the colour and pattern of its upper side to match the seabed and often flicks sand over its body to hide further, leaving just the eyes exposed. Lying still and concealed, it ambushes passing prey and avoids predators. Flounders swim with an undulating, rippling motion of the body and fins, gliding low over the bottom. The eye-migration that reshapes the larva into a flatfish is one of the most striking transformations in the fish world.

Human Interaction & Conservation

Flounders and other flatfish are important food fishes caught around the world, and their camouflage and unusual anatomy fascinate scientists and divers. Many populations support fisheries; some are affected by overfishing and habitat degradation, so status varies by species and region. Consult NOAA Fisheries and the IUCN Red List for current status.

More photos of the flounder