Review of Development and Aging in the Eye of Teleost Fish

Abstract

The teleost eye is an excellent organ for studying retinal development since teleosts and their eyes continue to grow throughout life. The retinal growth zones are found at the periphery of the eye and in some species also along the ventral embryonic fissure. The retinal cones are arranged into regular mosaic patterns, which is an advantage for microspectrophotometrical analyses of visual pigments. They revealed that teleost eyes are di-, tri- and tetrachromatic. The last type includes ultraviolet-sensitive cones. They appear in early life over the whole retina and later disappear in this region although they continue to be formed in the peripheral growth zones, but die there once the retina is differentiated. The melanin granules in the pigment epithelium and the cones and rods undergo circadian retinomotor movements. Another circadian rhythm is displayed by the tips of the photoreceptor outer segments, which are shed by cones at night and by rods during the day. The embryonic development of the retina is described in detail for the viviparous guppy, the salmonids and the zebrafish, which display direct development. This is contrasted by results of teleosts with indirect development (involving metamorphosis).