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Any of a class of purple, light-sensitive pigments similar to rhodopsin, found in the retinal rods of the eyes of freshwater fishes and certain frogs.
[Greek porphurā, purple dye, purple garment; see purple + opsin.]
(Biochemistry) a purple pigment occurring in the retina of the eye of certain freshwater fishes
[C20: from Greek porphura purple + -opsis + -in, on the model of rhodopsin]