Published: 5 December, 2001

Do fish see in color?

Do fish see in color?

There is not just a single answer to this question since not all fish have been tested for color vision. However, the common goldfish certainly sees in color and many more at least have the necessary nervous system elements for color vision to be present. Color vision is the capability to see and recognize objects based not on how bright they are, but on how well they absorb, reflect or transmit light of different colors. For example, an apple looks red in sunlight because all but the red part of the white light from the sun falling on it is absorbed by the apple's skin leaving only the red light available for vision.

In order to have color vision, the retina in the back of the eye must have color detectors, called cones, present and the brain has to be wired to make use of the information it gets from the cones. We have three different kinds of cones in our eyes, called red, green and blue that make human color vision possible. The goldfish has four kinds of cones: red, green, blue and ultraviolet. Other fish have different numbers and kinds of cones meaning that they have the capability of seeing in color. However, simply finding cones in the eye does not mean that an animal has color vision. You have to test it behaviorally to see if it can tell one color from another. For example, I could set up a tank with two windows at one end whose color I could change. I would start by making one window gray, that is having no color, and the other red. Whenever the fish went to the red window I would give it some food. I would change the brightness of the gray and red windows to make sure that the fish was training to only color. As soon as the fish had learned to associate red with food, I would start to replace the gray with other colors and see if the fish still only went to the red. This would be repeated for lots of different color combinations. If the fish remained true to its trained color, than it would be said to have color vision. To date, this kind of testing has only been done for a few kinds of fish. However, I am confident that as we test many more kinds of fish we will find color vision to be very common.