Studies on the eyes of New Zealand parrot-fishes (Labridae)

Abstract

Abstract An investigation was made of the pigment epithelium and photoreceptor layer of the eyes of New Zealand parrot-fishes Pesudolabrus miles, P. celidotus and P. pittensis (Labridae). Eyes were studied by light and electron microscopy, and characteristics of the retinal pigments were investigated. The pigment epithelium contains numerous melanosomes in the basal region of the cell and red cylinders within the processes. Melanosomes and cylinders are dispersed slightly vitread during light- adaptation. The photoreceptors comprise long single cones, short single cones, double cones and rods. The cones possess a lateral sac connected to the outer segment, and well-developed calycal processes arising from the ellipsoid. Rods are without a lateral sac and have fewer and less regularly arranged calycal processes. The membranes of rod lamellae stacks are more widely spaced than those of cones and are deeply dissected by a few longitudinal fissures. Cones form a regular mosaic of squares throughout the depth of the retina scleral to the external limiting membrane. Rods are numerous and distributed throughout the cone mosaic with no particular patterns. Cones undergo only very limited radial movements, and long single cones are always buried in the pigment epithelium where they are surrounded by red pigment. Rods shorten in darkness and come to lie inside the pigment epithelium. The red material in the cylinders is apparently a new pigment; it absorbs strongly below 560 nm, and prevents all but red light from reaching the long single cones and the rods when extended. Several features and consequences of this organization are discussed.