What fish genus is commonly called four-eyed fish?

The fish genus commonly called four-eyed fish is Anableps.

Anableps is a genus in the family Anablepidae. Its members appear to have four eyes because each eye is divided into an upper and lower portion by a band of tissue. The upper half is adapted for seeing through air, while the lower half looks through water. A surface-swimming fish can therefore monitor both environments at once without constantly raising or lowering its head.

The name is misleading in one important way: these fish have two eyes, not four separate eyes. Each eye has two pupils and two corneal regions that direct light to different parts of a shared optical system. The lens and retina are specially adapted to handle the different ways light bends in air and water.

Four-eyed fish live mainly in fresh and brackish lowland waters from southern Mexico through Honduras and northern South America, with populations also on Trinidad. They are livebearers and often feed at the surface on terrestrial insects. They should not be confused with the unrelated brownsnout spookfish or with “false four-eyed fish,” a name used for some Asian and Australian mullets.