PHOTORECEPTOR MORPHOLOGY AND VISUAL PIGMENT CONTENT IN THE PINEAL ORGAN AND IN THE RETINA OF JUVENILE AND ADULT TROUT, SALMO-IRIDEUS

We performed microspectrophotometric measurements on isolated retinal and pineal photoreceptors of the trout Salmo irideus. Retinal rods contain a visual pigment with lambda(max) at 512 nm. In adult trout the retinal cone system consists of single and double cones with pigments having peaks at 453 nm (single cones and one member of double cones), 530 nm (single cones and one member of double cones) and 598 nm (one member of double cones). Juvenile fish possess an additional type of single cone absorbing maximally at 400 nm. Scanning electron microscopy analysis of the cone mosaic shows a square pattern of double cones with a central single cone and corner single cones in yearling trout, and a similar pattern without corner single cones in two-year-old trout. Our data on the pineal organ reveal two different kinds of cells showing two distinct types of pigments, the former having its lambda(max) at 463 nm and the latter with its maximum at 561 nm.