Britannica Sources used in this answer

How are adult flatfishes different from most other fishes in body symmetry?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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*).

Adult flatfishes, which belong to the order Pleuronectiformes, are distinct from most other fishes and vertebrates because they are asymmetrical. While most vertebrates exhibit bilateral symmetry, adult flatfishes are strongly compressed and possess both eyes on a single side of their head.1

This unique body structure develops during a metamorphosis phase. Although larval flatfishes begin with one eye on each side of the head, one eye migrates to the opposite side as the fish matures and prepares to settle on the ocean floor. This migration involves significant osteological changes, including the twisting of the skull, frontals, and mouthparts. Consequently, the adult fish typically features a pigmented ocular side and an unpigmented, blind side that rests against the bottom.21