The Anableps anableps is an odd fish in more ways than one. It is a surface-dwelling fish that rarely swims around underwater, though it will dive if it feels threatened. It grows to some 12 inches in length, with mature females growing larger than males. Their generally cylindrical body has an olive-brown back. The flanks and belly are a lighter cream color with four narrow parallel dark stripes that begin behind the large pectoral fins decorating the flanks. The most noticeable feature of this fish are the two large, bulbous eyes that protrude from the small head. Observed from above, the eyes and back of this fish continuously break the water line.
Since just two eyes are visible, where does Anableps anableps’ common name of four-eyed fish come from? Being a surface-dwelling fish, it does have to beware of predators, such as birds from above, as well as larger fish from below. To cope with this, Anableps anableps has large eyes (half of which are submerged as the fish floats on the water surface) that are divided into two parts. The lower half of each eye contains its own pupil, which is adapted for perfect vision underwater, while the upper half of the eye with a second pupil offers clear vision of life above water. Hence, the common name of four-eyed fish is quite relevant. Its above-water vision is excellent for scanning the water surface for insects that fall into the water, which make up its preferred choice of food.
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