>>857741>>857835They see red.
The three types of cones in the human eye each contain a photo-sensitive pigment that has the capacity to absorb a range of light wavelengths. Each cone is characterized by the wavelength at which maximum or peak absorption occurs. The three are as follows:
erythrolabe; peak absorption at 565nm; red
chlorolabe; peak absorption at 535nm; green
cyanolabe; peak absorption at 440nm; blue
Light wavelength is measured in nanometers and the visible spectrum ranges from 700nm (red) to 400nm (blue-violet).
Trout Eyes:
Trout, on the other hand, have four receptors, and the four peaks are 600nm, 535nm, 440nm, 355nm.
The second and third conform to the green and blue cones in humans. The first is similar to the human red, but its sensitivity range includes longer wavelengths than humans. The fourth is outside the band of wavelengths visible to humans and is referred to as "ultra-violet". However, the fourth class of cones disappears by the time a trout is two years old.
