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How do flatfishes match the colour of the seafloor?

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Body plan and sexual dimorphism in the common sole (Solea solea) and dusky flounder (Syacium papillosum). — pleuronectiform Body plan and sexual dimorphism in the common sole (*Solea solea*) and dusky flounder (*Syacium papillosum*).

Flatfishes are well-known for their remarkable ability to camouflage themselves by matching the color and pattern of the seafloor on which they rest. This adaptation is a form of background matching that helps them avoid predation.12

The mechanism behind this rapid color change involves specialized branched cells called chromatophores, which are located in the fish's skin. When a flatfish adapts to a change in its environment, it redistributes the pigment within these cells. While some color adjustments occur slowly through long-term changes in the number of pigment cells or the amount of pigment they contain, the ability to blend in with a new background is primarily achieved through this rapid redistribution of pigment within the cell boundaries.3

Typically, the ocular (upper) side of the flatfish is pigmented to facilitate this mimicry, while the blind (bottom) side remains unpigmented.42