Fish are asleep, but not all. In addition, they are not asleep in the literal sense of the word.
The fact is that they can not rest like people, because of the physiological structure of the eye and the absence of a swimming bladder in some species of fish.
How do fish sleep?
To any person in order to fall asleep,You need to close your eyelids. Fish do not have eyelids that they could close, falling asleep with a sound and healthy sleep. However, this does not prevent them from resting, which is called "fish-like". Some of them even lie on their side. In fact, they do not close their eyes.
It can not be said that the fish are inUnconsciousness, like a person during sleep. Yes, their minds are blunted, but not so much. Physical functions are suspended for a while, and the fish itself can not pay any attention to what is happening around. However, with all this, the brain receptors are in combat readiness, which allows it to instantly get out of its numbness.
Great variety of species of fish on Earth. Many of them have certain periods of activity and rest. "Sleep", while remaining afloat, they are helped by a swimming bladder. It should be noted that this organ is not available for all fish, so some of them generally have to sleep in motion. These include all bottom and deep-water fish species. "Dream" with them is a short respite during their continuous movement. That is why the "sleep" such a holiday can be called conditionally.
Without sleep and without rest
One of the prominent representatives of bottom fish, notHaving a swimming bladder are, of course, sharks. In order not to drown during sleep, these predators need to actively swim. Unlike man and many terrestrial animals, for whom swimming is a rather short-term occupation, sharks are forced involuntarily to be in constant movement from the first day of their lives to the last!
Absence of a swimming bladder does not allowSharks should always remain in a "suspended" state in the depths of the depths, as many other species of fish can do. If the shark at least for a moment stops its wave-like movements with muscular fins and an outstanding tail, then the gravity of its own body will inexorably pull it to the bottom! Curiously, that's why dead sharks never surface, but fall to the bottom.
As already mentioned above, in the traditional senseThese fish never sleep. They are in constant flux both day and night. However, some of them can still rest. Special species of sharks living in the coastal waters swim in small underwater caves located in shallow depths of rivers or lakes. There they lie on rocky ledges or on the bottom.
It can be concluded that in the literal senseThis understanding does not sleep any fish, but some lucky ones, whom God has awarded with swimming bubbles, yet can afford to somehow relax, which can not be said about bottom and deep-sea fish.