The four-eyed fish are a genus of approx. 30 cm long viviparous toothcarps that are common in the muddy coastal waters of northern South America and on the Pacific coast of Central America.
Clear view above and below the water
The eyes of the four-eyed fish are divided into two halves by a transverse partition. So the fish can see both underwater and above water. The upper half of the lens is weak, the lower half strongly curved to ensure the correct refraction of light. It is the only known vertebrate that can see clearly above and below water at the same time.
The four-eyed fish have a rather strange-sounding division of the genital organs, so that the breeding of the fish is often more difficult: The genital organs are not in the middle on the underside of the body, but either left or right on the side of the four-eyed ish. A “left male” can only mate with a “right female” and vice versa.