A SHORT-WAVELENGTH SENSITIVE CONE MECHANISM IN JUVENILE YELLOW PERCH, PERCA-FLAVESCENS

The retinal cone mosaic of adult yellow perch, Perca flavescens, consists of square units each having a central single cone surrounded by four identical twin cones. No cones are present at the corners of the square units. However, the cone types and organization of the retinal mosaic in juvenile P. flavescens has not been thoroughly described. We report here the presence of small, single cones at the corner positions of the square units in juvenile P. flavescens. Not every corner, nor every unit has these cones, and their distribution over the retina is not uniform. Microspectrophotometry places the visual pigment absorbance maximum of these short single cones in the region of 400 nm. Electrophysiological measurements of spectral sensitivity demonstrate a short-wavelength mechanism in juveniles that is absent, as are the small corner cones, in adults. Possible advantages of such a mechanism to juvenile perch are discussed.