Morphology and spectral sensitivities of retinal and extraretinal photoreceptors in freshwater teleosts

Fish eyes possess a complicated morphological and neural organisation of re tinal and extra-retinal receptors. Features such as photoreceptor mosaic ar ray and photoreceptor grouping are unique among vertebrates. Spectral sensi tivities of these photoreceptors range from UV to the red portion of the vi sible spectrum. Moreover, these sensitivities can change with the age of th e animals. In this review we will examine thoroughly the morphology, and th e spectral sensitivities of retinal and extra-retinal receptors and the inf luence upon them of factors such as hormones, ageing, season, habitat light conditions, and migration. (C) 1999 Elsevier Science Ltd. All rights reser ved.