What do fish see underwater?

The lens sits inside the eye. In many fish it is almost spherical and focuses light on the retina, the light-sensitive layer at the back of the eye. To focus, it moves relative to the retina rather than changing shape as ours does.

A lens that changes shape very little does not mean that a fish necessarily sees distant objects out of focus. Clarity depends on its visual system, as well as on light and particles in the water.

Schematic illustration of focusing by lens movement.
Schematic illustration of focusing by lens movement. © dive.explo360.fr — All rights reserved. Reproduction prohibited without permission.

What is a fish’s field of view?

Field of view
Fish vision is only one aspect of their perception of the environment. © dive.explo360.fr — All rights reserved. Reproduction prohibited without permission.

Eyes placed on the sides give many fish a wide field of view. Its extent varies between species, however: fish should not all be described as having 360-degree vision.

The area seen by both eyes at once is called the binocular field. It can help locate prey. Movement and other visual cues also contribute to judging distance.

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