Which fish has both eyes on the same side of its head?

The fish with both eyes on the same side of its head is the flatfish. This unusual arrangement develops as a flatfish transforms from a symmetrical, free-swimming larva into a bottom-dwelling juvenile.

During metamorphosis, one eye gradually migrates across the top of the head. The adult then rests on one side, with both eyes facing upward to watch for prey and predators. The lower-facing side becomes the pale “blind side,” while the upper side is often better camouflaged.

Flatfish is a broad group that includes flounders, soles, turbots, halibut, and plaice. Different families develop different orientations: some are left-eyed and others right-eyed. That variation is why “flounder” is not always the best answer to this general question.

A common mix-up is with skates and rays. They are also flattened marine animals, but their eyes remain on opposite sides of the head. Eels, meanwhile, have a long symmetrical body and conventional paired eye placement.