Allen, Donald M.; McFarland, William N.; Munz, Frederick W.; Poston, Hugh A. 1973. Changes in the visual pigments of trout. Canadian Journal of Zoology. 51(9): 901-914.
The proportions of two visual pigments (rhodopsin and porphyropsin) were examined in four speciesof trout under experimental and natural conditions. Brook trout (Salvelinus fontinalis), rainbow trout(Santo gairdneri), and brown trout (Salmo truita) have different relative proportions of visual pigmentsin their retinae. The visual pigment balance in wild cutthroat trout (Saint() clarki) is related to forestcanopy (access to light) and season. The brown trout have a more red-sensitive and less labile pair ofvisual pigments than brook or rainbow trout, which respond to photic conditions by increasing the pro-portion of porphyropsin (in light) and increasing rhodopsin (in darkness). The brown trout have a highpercentage of porphyropsin, regardless of experimental conditions. This result does not reflect an in-ability to form rhodopsin but rather may relate to a consistently high proportion of 3-dehydroretinol inthe pigment epithelium. The possible advantages and mechanisms of environmental control of troutvisual pigment absorbance, as currently understood, are discussed.