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

Fish eyes possess a complicated morphological and neural organisation of retinal and extra-retinal receptors. Features such as photoreceptor mosaic array and photoreceptor grouping are unique among vertebrates. Spectral sensitivities of these photoreceptors range from UV to the red portion of the visible spectrum. Moreover, these sensitivities can change with the age of the animals. In this review we will examine thoroughly the morphology, and the spectral sensitivities of retinal and extra-retinal receptors and the influence upon them of factors such as hormones, ageing, season, habitat light conditions, and migration.