Rest is necessary for all animals, however on appearance of some of them it is impossible to tell, they sleep or not. Similar difficulties are observed, for example, with fishes. Even during sleep their eyes remain open that often confuses people and does not allow to interpret a state correctly.
Why fish does not close an eye
Fishes, as well as other representatives of fauna, sleep. Only they at the same time do not close an eye. All because fishes simply have no century. This difference from the person and land fauna is caused Wednesday in which they live. People should humidify constantly an outer sheath of an eye, blinking. In a dream to do it very difficult therefore eyelids densely close a cornea, saving it from drying. Fishes live in water which already does not give them to an eye to wither. Additional protection is not required to them.
Eyelids are available only for some sharks. During attack the predator blinks, thereby protecting an eye from damages. A shark which have no century roll up eyes.
As bony fishes sleep
Aquarians sometimes can observe how their pets lay down on soil or seaweed, fade a paunch up or perpendicularly a bottom. However it is worth making the sharp movement or to turn on the light as pets begin to swim again, indifferently. Dream of all fishes very sensitive. The majority of types choose the quiet secluded place for a dream, however all have habits. For example, the cod can settle sideways on a bottom, a herring – to hang in the thickness of water-headed down, the flounder – to bury in sand. Bright tropical fish parrot – the big original. Preparing for sleeping, she constructs around herself a cocoon from slime which, most likely, does not allow predators to find it on a smell.
All species of fish, depending on time of their activity, can be divided into day and night.
As cartilaginous fishes sleep
The structure of bony and cartilaginous fishes differs. Cartilaginous fishes whom sharks and slopes treat have no covers on gills, and water in them comes only to time of the movement. Because of it it was impossible to have a sleep quietly at them. However during evolution they managed to adapt and snatch to themselves hours for rest. Some types got bryzgalets – special bodies behind eyes by means of which fishes involve water and direct it to gills. Others prefer to choose places for a dream with a strong benthonic current or sleep, constantly opening and closing a mouth, thereby allowing water to oxygenate blood. The shark a spiny dogfish living in the Black Sea sleeps on a clothes line at all. The spinal cord is responsible for the movement at her, head can have a rest at this time. Also scientists consider that some representatives of cartilaginous fishes can sleep in the manner of dolphins, serially "disconnecting" that right, that left hemisphere.