Visual pigments in marine teleosts:
adaption to different environments
dr. scient. Jon Vidar Helvik
Research scientist
One of the fascinating and challenging aspects of studying the sensory system in fishes is that their perception is different from ours and may escape our sensory abilities. Visual capabilities in teleosts are adapted to a great diversity of photic conditions.
Retina, the light sensitive region of the eye contains a vast array of photoreceptor cells that transform the light photon into neural signals. Two types of photoreceptor cells in the vertebrate retina are responsible for this light detection: rods and cones. The cone cells function during daylight and are responsible for color vision, while the rod cells are responsible for vision under low light condition. The visual pigment (opsin) is a protein of about 350 amino acids surrounding a chromophore (retinal). Both, the amino-acid sequence of the opsin and the nature of the chromophore (Vitamin A1 or A2) tune the absorbance spectrum from ultraviolet (~350 nm) to red (~650 nm). Visual pigments can be divided into five major groups: UV-, blue-, green- and red-light sensitive (cone opsins) in addition to the rod opsin.
Since the spectral sensitivity of a photoreceptor cell is mainly a result of the primary structure of the photo pigment, there seems to be a direct relationship between the primary structure of the visual pigment and the light environment an organism live.
The aim of our studies is to outline the molecular nature of visual pigments in marine fishes and relate the expression of these molecules to life stages, function and adaptation to photo environment. The four marine teleosts: Halibut, turbot, cod and herring have been chosen for this comparative analysis of the visual pigments. The larvae from these species are located in the same pelagic environment (in the upper photic zone) while their later juvenile stages adapt different life styles in different environment.
Freshwater fishes such as goldfish and zebrafish are used as models for visual system development in vertebrates. Typical for many freshwater teleosts are that they follow a direct development program where the embryos hatch at an advance state with a retina containing both rod and cones. Many marine fishes have a more indirect developmental program with a pelagic larva stage where retina consists of only cone photoreceptors and an adult retina with rods appears after metamorphosis. Flatfish like halibut and turbot offers therefore a very interesting model for studying mechanism of retina differentiation.
We have cloned several opsins form different marine teleosts and used the expression of these opsins to analyse their visual system. We have shown that flatfish like halibut and turbot have special photoreceptor cells in the ventral retina detecting UV light at the larval pelagic stage, while a new group of UV sensitive cells appear in the dorsal retina during metamorphosis in the period when the species changes to a benthic life form.
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| (+47) 555 84371 | (+47) 555 89683 | vidar.helvik@mbi.uib.no |
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