title: Retinal organization of the eyes of three nototheniid fishes from the Ross Sea (Antarctica).
abstract: The retinas of 3 nototheniid fishes co-existing in the McMordo Sound (Antarctica), but with different depth preferenda, were studied to establish a correlation between habitat and retinal organization. Light and electron microscopic observations of the retinas of these fishes show the layering typical of most vertebrate retinas. However, the difference in the ratio of rods and cones, and particularly the structure of the rods are related to the amounts and spectral properties of the light available in the depths in which they are meant to operate. D. mawsoni possesses the highest concentration of unusual rods characterized by long cylindrical inner segments (60 microns) and outer segments. T. borchgrevinki has the smallest number of rods, while T. bernacchii possesses an intermediate number. The retinal pigmented epithelium is present in the 3 retinas studied, but it is only in T. borchgrevinki that there is an apparent movement of pigment granules (photomechanical response). Thus, the retinal organization of T. borchgrevinki suggests that this species is able to see in an environment that is relatively bright but in which ambient light levels can change. On the other hand, the apparent lack of photomechanical movements and the greater population of rods in T. bernacchii and especially D. mawsoni suggest that these 2 species are better adapted to an environment of constantly low light intensities.
mesh_terms: D000818:Animals; D000864:Antarctic Regions; D005399:Fishes / Q000033:anatomy & histology*; D008854:Microscopy, Electron; D010786:Photoreceptor Cells / Q000648:ultrastructure; D010857:Pigment Epithelium of Eye / Q000648:ultrastructure; D012160:Retina / Q000033:anatomy & histology*; D013045:Species Specificity