Double vision
- University of California, Davis, Department of Ophthalmology, 4860 “Y” Street, Suite 2400, Sacramento, CA 95817, USA; irschwab@ucdavis.edu
Most animals have evolved eyes that focus in air or in water. Some have evolved eyes to have an aerial or aquatic view at different times (see BJO cover July 2002), but few species indeed have evolved a design that can focus in both media simultaneously. Anableps anableps (from the Greek meaning “enlarged eye”) does just that.
“Cuatro Ojos,” as the fish is known in Brazil, seems to be so odd as to be unbelievable. But these incredible fish, and their close relatives, have evolved the necessary adaptations to prosper as intertidal specialists, and can be found in fresh, brackish, or even pelagic waters.
There are three different species of Anableps and while the ecology of the three differ somewhat, each has similar environmental needs for multiple eyes with similar ocular design. All three species grow to a maximum of 30–35 cm and resemble flat, floating cigars with large eyes with the long axis of the body of the fish parallel to the surface of the water.
All of these fish can see simultaneously in air and water using a unique ocular design, as can be seen …
