Four-eyed fish

Four-eyed fish are surface-dwelling fishes of the genus Anableps. Each eye is divided into upper and lower optical regions, allowing simultaneous vision above and below water.

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Anableps eye: The divided eye of an Anableps fish, with distinct regions adapted for viewing above and below water. Its two pupil regions let the fish monitor both environments at once.
Surface feeding: Feeding on food found at or near the boundary between air and water. Four-eyed fish can watch for prey above the surface while remaining alert underwater.
Anableps: A genus of livebearing fishes native to tropical parts of Central and South America. Four-eyed fish is the common name for members of this genus.
Anableps anableps: A species of four-eyed fish native to the Atlantic coast of South America. It is the best-known Anableps species and exemplifies the divided-eye adaptation.
Refraction: The change in a wave’s direction as it passes between materials with different optical properties. Light from above and below the surface bends differently, shaping the eye’s two viewing regions.
Mangrove forest: A coastal ecosystem dominated by salt-tolerant trees rooted in tidal, often muddy waters. Mangrove channels are among the brackish habitats occupied by Anableps.
Teleost: A diverse group of bony fishes whose skeletons are largely made of bone. Anableps belongs to the teleost radiation of modern bony fishes.
Anableps microlepis: A species of four-eyed fish found along the northern coast of South America. Its distribution provides another example of the genus’s tropical coastal range.
Cornea: The transparent front surface of the eye that helps focus incoming light. Anableps has upper and lower corneal regions adapted to air and water.
Estuary: A coastal body of water where river freshwater mixes with seawater. Several Anableps species inhabit estuaries and other changing coastal waters.