Fish
Peacock Flounder
Bothus lunatus · also called plate fish, flowery flounder
The peacock flounder is a fish that lies down for a living. It hatches looking like any other fish, then rebuilds its own skull so that both eyes end up on one side, and spends its life pressed flat against the seabed, changing colour to match whatever it is lying on.
Overview
Peacock flounders live on shallow sand flats, seagrass beds, rubble, and reef margins throughout the tropical western Atlantic and Caribbean. They are bottom-dwellers, resting flat on the sand — often partly buried — and moving over it in short glides or by “walking” on their fin rays. They are active by day, and each male defends a territory containing several females, courting and signalling by flicking up one pectoral fin like a raised flag.
Becoming flat
A young peacock flounder starts as a normal, symmetrical, swimming fish. Then, over its first weeks, an extraordinary transformation occurs: the right eye migrates across the top of the head to join the left one, the skull and jaw twist, the body flattens, and the fish tips onto its right side and sinks to the bottom. The upper (left) side develops eyes, colour, and pattern; the lower (right) side goes pale and blind. From then on the flounder is a one-sided animal.
Instant camouflage
The peacock flounder is one of the fastest and most convincing camouflage artists among fish. By adjusting pigment cells in its skin it changes both colour and pattern, matching sand, gravel, mottled reef, or seagrass, and it does so in two to eight seconds. Laid on an artificial checkerboard, it will attempt the checkerboard. It uses its raised, independently swivelling eyes both to spot prey and predators and to read the background it needs to imitate.
Hunting
Buried and colour-matched, the flounder is an ambush predator, lunging from stillness to grab small fish, shrimp, crabs, and worms that stray within reach, then settling back and vanishing again.
Status
The peacock flounder is Least Concern and common. It is caught only incidentally and is not a significant fishery target. Its role is as a mid-level predator on soft-bottom habitats, and as one of the reef’s best-loved demonstrations of camouflage for divers and photographers.
Peacock Flounder: common questions
How does a flounder end up with both eyes on one side of its head?
A peacock flounder hatches as an ordinary, upright, bilaterally symmetrical fish with one eye on each side. As it grows over its first weeks, its skull remodels and the right eye gradually **migrates up over the top of the head and around to the left side**, while the fish tilts onto its right flank. By the time it settles to the bottom it is a flat, one-sided fish lying on what was its right side, with both eyes now pointing up and its underside (the old right side) pale and blind. This transformation is one of the most dramatic developmental changes in any vertebrate.
How good is the peacock flounder's camouflage?
Among the best of any fish. It changes both colour and pattern by expanding and contracting pigment cells in its skin, and it can complete a match to a new background in as little as two seconds and always within about eight. In a famous experiment, a peacock flounder placed on a chessboard produced a passable checkerboard pattern on its own body. It reads its surroundings with its eyes; a flounder that is blind on one side cannot camouflage that side properly.
How does the peacock flounder hunt and hide at the same time?
It buries itself by flicking sand over its body with its fins until only the raised, independently swivelling eyes are exposed, then waits. Small fish and crustaceans that wander close are seized in a quick lunge. Lying flat, colour-matched, and half-covered, the flounder is nearly invisible to both its prey and its own predators — barracuda, groupers, and larger fish that would happily eat it.
Are peacock flounders good to eat, and are they fished?
They are edible and taken incidentally in some Caribbean fisheries and by spearfishers, but they are small and thin and not a major commercial species. The peacock flounder is listed as Least Concern and remains common. Its main value is ecological — as a mid-level predator on sand flats — and as a favourite subject for divers and underwater photographers because of its camouflage and its habit of "walking" over the bottom on its fin rays.