Long-wavelength visual pigment polymorphism, similar to that found in primates, was found in the guppy using microspectrophotometry (MSP). Guppies have a rod pigment with a wavelength of maximal absorbance (lambda max) at 501 nm and cone pigments with peak absorbance at 408 and 464 nm. In addition individuals may have one, two or three cone classes in the yellow-green region of the spectrum with mean lambda max values of 533, 543 and 572 nm. Unlike primates this variation is not sex-linked and may be based on only two visual pigments which occur either on their own in outer-segments of the 533 nm and 572 nm cone classes or as a mixture in the 543 nm cone class.