Molecular mechanism of visual adaptation in fish
2005
Minamoto, T.(Kyoto Univ., Otsu (Japan). Center for Ecological Research) | Shimizu, I.
Research articles on the molecular mechanisms of fish visual adaptation are reviewed in addition to present studies on the visual pigments of ayu (Plecoglossus altivelis). To adapt to various photic environments, fishes use three main strategies of molecular mechanism: (1) changing the ratio of Al/A2 retinal in the chromophore; (2) mutation of opsin genes resulting in changes to the amino acid sequence of opsin protein; and (3) changing the expression patterns of opsin genes. Amphidromous fishes change the retinal ratio according to their habitat and adjust the absorption maximum (lambda-max) of rod-opsin to environmental light. The same phenomenon has been observed in landlocked ayu in Lake Biwa. Various fish species inhabiting deep seas or lakes, at depth that very little blue light can reach, have rod-opsin with lambda-max of about 480nm. Some fishes including African cichlids, eels and ayu, utilize different sets of visual systems, combining cone opsins so as to adapt to diverse habitats. Fishes have apparently evolved a visual system with high plasticity, being visually adapted to various environments by combining such molecular mechanisms. Fish receive light not only via visual cells in the retina, but also via non-visual cells in both the retina and extra-ocular organs. In addition to visual opsins, non-visual photoreceptive opsins of fishes are also reviewed.
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