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How does a larval flatfish change as it becomes an adult?

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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*).

During their development, larval flatfish (order Pleuronectiformes) undergo a dramatic transformation known as metamorphosis to transition from a symmetrical, free-swimming larval stage to an asymmetrical, bottom-dwelling adult existence.12

Initially, larval flatfish are bilaterally symmetrical, possessing one eye on each side of the head. As they grow, they undergo a period of rapid body change where one eye migrates to the other side of the head. This migration occurs either over the middorsal ridge or through the head, involving significant structural changes to the skull, including the shifting of frontal bones and the twisting of mouthparts.13

Once this migration is complete, the fish settles to the bottom to assume a benthic lifestyle. The adult fish then habitually rests on its side, with the "ocular" (eyed) side facing upward and the "blind" side facing the bottom. This ocular side typically develops pigmentation to help the fish blend into its surroundings, while the blind side usually remains unpigmented.1243