How does a common carp see the world?

The common carp is a tetrachromat with ultraviolet, blue, green and red cone channels. Direct cell measurements found peaks at 377.5, 458, 532 and 600 nanometres, while adult retinal anatomy gives an estimated 3.60 cycles per degree of resolving power. Microspectrophotometry measured four cone classes, and conditioning in the same group of fish found a behavioural ultraviolet sensitivity peak near 380 nm under a long-pass background.

Microspectrophotometry measured four cone classes, and conditioning in the same group of fish found a behavioural ultraviolet sensitivity peak near 380 nm under a long-pass background. Tetrachromat with ultraviolet-, blue-, green- and red-sensitive cones plus rods

Adult retinal anatomy gives an estimated upper resolving power of 3.60 cycles per degree, not a behavioural threshold. A species-level total field, binocular overlap and critical flicker value were not established, so no number is assigned to them.

Its eyes resolve about 3.6 cycles per degree against your 60, so a face has to be roughly 17 times closer for it to pick out the detail you do. Your outline and your movement read clearly; your expression does not.

Rods and retinal dark adaptation are present, but the cited studies did not establish a behavioural night-vision threshold.

Four cone classes spanning ultraviolet to red. Behavioural ultraviolet action spectrum measured in three conditioned carp. Adult anatomical resolving power estimated at 3.60 cycles/degree; field and CFF remain unquantified. Researchers measured the ultraviolet action spectrum by conditioning three carp and then measured ultraviolet cones from the same group. The behavioural and cellular peaks agreed, linking a receptor to a demonstrated response.

Humans normally use three cone classes and our lenses block ultraviolet; common carp use four cone channels extending into ultraviolet. An RGB screen can show only visible false colour and reduced detail, never the extra channel itself.