[The perceptive color space in the carp (Carpio cyprinus L.)]. 
Discrimination of colours was studied using choice conditioning paradigm (one of a pair of colour stimuli) in carps.  Matrix of probabilities of instrumental reactions (catching a bead) was constructed by the results of eight experimental sessions with successive reinforcement of one of the eight colours.  It was processed by factor analysis.  The spherical structure of carp's perceptual colour space revealed by factor analysis was similar to that of monkeys and humans.  Four eigenvectors which constituted four-dimensional Euclidean hypersphere corresponded to excitation of four colour-encoding neuronal channels, i.e., red-green, blue-yellow, bright and dark.