Organs of vision - have a typical vertebrate structure. Distinctive features of the fish eye are a flattened cornea, cartilaginous sclera, globular lens and sickle-shaped outgrowth, with the contraction of which the lens is pushed deep into the eye. Between the vascular and protein shell has a silvery shell, giving the eye a greenish-golden luster. There are no eyelids only in mullet, southern herring have a fatty eyelid in the form of a transparent film covering the eyes. There is a blinking membrane in the shark. In cave fish eyes are reduced or disappear completely. In deep-sea fish eyes reach huge sizes, some become telescopic, which increases their sensitivity, expands the field of vision and allows you to catch the weakest light. Fish are myopic, the maximum range of vision does not exceed 15 m (predators), bony and lampreys distinguish colors, rays and stingrays - do not distinguish.
The eyes of fish are very similar in structure to the eyes of other vertebrates. An important difference between fish eyes and mammalian eyes is that fish do not change the curvature of the lens for accommodation, but bring it closer to the retina or farther away from it. The structure of the retina in fish varies depending on where they live: in deep-sea species, the eyes are adapted to perceive light mainly in the red part of the spectrum, while fish that live in shallow waters, perceive a wider spectrum. In some deep-sea fish, such as pearl-eyed, the eye has a telescopic structure that allows to capture in the dysphotic zone (twilight zone) of the ocean the minimum light. In addition, these fish have a completely unique "pearl organ", which outwardly represents a white spot on the surface of the eye, which, being associated with the secondary retina, noticeably expands the sector of the normal field of vision of fish. There are also many species of blind fish - marine deep-sea or freshwater "cave" (subterranean) fish that have lost all or part of their vision function. In 2011, another new species of such blind fish, Bangana musaei, was discovered.
Organs of vision
Tags: organs of vision