[Scotopic visual pigments in 3 Percidae: Perca flavescens, Stizostedion vitreum and S. canadense]

The scotopic visual pigments of three percids from Quebec waters, viz. the yellow perch (Perca flavescens), the walleye (Stizostedion vitreum) and the sauger (S. canadense), were studied in situ using a microspectrophotometer-computer complex. The difference spectra show that the three fishes possess a porphyropsin whose lambda max. is at 530 nm in the yellow perch, 533 nm in the walleye and at 536 in the sauger. This variation corresponds to the tendency of the visual pigments to fit the preferred environments. The three species studied also have different modes of life. The yellow perch inhabits mostly shallow, clear waters while the walleye and sauger prefer turbid waters. The retinal structure and responses also differ among them. Since the difference in lambda max. is so small, the differences in habitat and behaviour may be attributed to morphological differences in the retina rather than to its visual pigment content.