It is difficult to imagine sleeping in water, and even surrounded by all kinds of predators. How do marine and freshwater inhabitants rest after a day’s activity?
Rest for aquatic inhabitants is vital. At this time, the brain is cleaned from the waste products of cells, DNA is repaired, damage to which inevitably accumulates.
In human understanding, fish never sleep.
Some species of fish, such as catfish or brocade carp, lose their vigilance to the point that they can be caught by hand. True, most species remain on guard and are able to instantly respond to danger.
Many bony fish with a skeleton, gills and swim bladder are motionless
It is much more difficult for sharks and rays to sleep: they lack gills and a swim bladder. In order for oxygen-rich water to enter the gill slits, they are forced to constantly move. While the brain is resting, the spinal cord provides movement.
In addition to fish, hundreds of other animal species live in the body of water. The dolphin family — dolphins, whales and killer whales — has probably adapted best of all to the habitat.
They have left and right brain hemispheres.
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