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What is sleep?
Almost all animals sleep: they do a matter of survival. Fish is no exception. But to understand it, you need to know that sleep can be defined in two ways.
The first definition of sleep depends on the electrical activity of the brain. at A study published in nature in 2019, researchers showed that during periods of immobility, zebrafish – often كثير It is used in medical researchShow two states similar to those in mammals (including humans), birds and reptiles: slow wave sleep and rapid eye movement (or rapid eye movement) sleep.
However, a Literature review 80 studies Published in 2019 in the magazine The brain, behavior and development confirms it Brain waves are poorly measured underwater And that fish do not have a cerebral cortex, which is the part of the brain where these waves are measured in humans. The researchers concluded that the evidence for sleep in sharks and rays – which breathe without swimming – is preliminary and that evidence for sleep in constantly swimming fish is not yet available.
However, the second definition of sleep remains: that it depends on behavior. Suggest that sleep is Reverse case of low reactionIt is usually associated with the absence of physical movements. Current knowledge shows that many fish meet this description.
Rest or sleep?
The There are 33,230 species of fish, depending on the organism fish base, but the behaviors related to sleep are similar to each other. At rest, fish either come to rest on the sea floor or near the surface, or swim slowly. Their breathing slows down and they have little or no reaction to what is going on around them. And if we don’t see them closing their eyes, it’s because they don’t have eyelids.
This period of inactivity can occur during the day or at night and has a variable duration. So Mozambique tilapia It descends at night into shallow water, slowing its breathing and freezing its eyes, while during the day the tendon sleeps on the sea floor for about twenty minutes.
a study Stanford University School of Medicine He points out that many fish seem to have sleep cycles and, like humans, produce the hormones that regulate these cycles.
This means that the fish who live in caves, where it is always dark, you have the opportunity to sleep with a regular circadian rhythm, which is different from that of fish that live on the surface. This was indicated by a study published in 2011 in current biology. Mexican troglodyte fish, or Mexican tetra, that live in caves can Reduce your need for sleep in times of famine. Other fish can reverse their sleep patterns when needed. This is the case of the white sucker that can become nocturnal when separated from its shallow waters, according to a study published in Canadian Journal of Zoology.
Where does the fish sleep?
Fish can float in place, get stuck in mud or coral, hide in the sand, or build shelter for themselves. hide predators. On the other hand, parrot fish find a shelter in which to rest after they rest secretes a cocoon of mucus around to protect itself from parasites.
But most fish cannot bear to remain completely still while they sleep. To breathe, they must strike their fins at twice their normal speed, to harvest the oxygen in the water. Others, such as sharks, must keep moving in order to maintain oxygen-rich water on their gills. This explains the persistence of the theory that fish do not sleep.
Rule
Fish don’t seem to sleep in the sense that humans understand it. This does not prevent some species from freezing themselves in a shelter, while others swim in slow motion, for longer or shorter periods of time allowing them to regain their energy.
Photo: Tambako/Flickr/CC