{"id":32893,"date":"2023-10-09T13:00:32","date_gmt":"2023-10-09T11:00:32","guid":{"rendered":"http:\/\/05196a17-e24d-43c8-aa71-50306333f4d5"},"modified":"2023-10-09T14:37:04","modified_gmt":"2023-10-09T12:37:04","slug":"do-fish-sleep","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcwildlife\/rss_feed\/do-fish-sleep\/","title":{"rendered":"Do fish sleep?"},"content":{"rendered":"

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By Stuart Blackman\n <\/p>

Published: Monday, 09 October 2023 at 11:00 AM<\/p>

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Knowing whether fish sleep or not for certain is quite tricky. Fish are inscrutable animals, at least to human eyes. It\u2019s difficult for us to read the body language of something that has no limbs, and there\u2019s not much to go on by way of facial expressions. <\/p>

The lack of eyelids doesn\u2019t help either, especially when it comes to telling the difference between a sleeping fish and an awake one.\u00a0<\/p>

Do all animals sleep?<\/a><\/li>
What animals sleep standing up?<\/a><\/li>
Which animal sleeps the most?<\/a><\/li><\/ul>
Do fish sleep?<\/h2>
Certainly, most fish routinely enter an inactive state that looks very much like sleep<\/strong><\/a>. This state may involve a single long period or several short ones over the course of a day, and it seems to happen more frequently during the night. <\/p>
A fish might rest on the bottom during these periods, or float motionless in the water column. Damselfish shelter among the branches of coral, while wels catfish have been recorded wedging themselves among the surrounding vegetation. And when parrotfish settle down for the night, they build a mucous chamber around themselves, which is thought to provide a barrier against parasites.<\/p>
None of this is proof that fish actually sleep. It could be that, being unable to feed or interact in the dark, they have little reason to do anything other than hunker down and save energy. Crucially, though, like sleeping reptiles, birds and mammals, fish in this state are less responsive to what\u2019s going on around them \u2013 they take longer to react to being prodded, for example, or offered food.<\/p>
There is also evidence that they need to sleep, which would seem to contradict the idea that they are just killing time. It has been shown, for example, that disrupting the inactive phase of a cichlid fish causes it to be less active the following day. And zebrafish respond to \u2018sleep\u2019 deprivation by making up for it at the next opportunity.\u00a0<\/p>
The biological function of sleep remains poorly understood, although it seems to play an essential role in consolidating memories of experiences accumulated during the waking hours. This might shed light on why some species of ocean schooling fish seem not to sleep at all. <\/p>
Certainly, mackerel and tuna would risk becoming separated from the group were they to doze off. They might yet turn out to sleep with one half of their brain at a time, much like dolphins sleep<\/a>. But another intriguing possibility is that the open ocean just isn\u2019t a very stimulating place to live, so they have few memories to process.<\/p>
Insomniac fish are rare exceptions, though. The fact that so many species do it suggests an ancient origin for vertebrate sleep. There does seem to be a major difference, though: there is little evidence that fish experience the REM sleep found in mammals, birds and reptiles, characterised by rapid eye movements and muscle twitching, and which is associated with dreaming in ourselves. So it might be that this particular mode of sleeping evolved after the terrestrial vertebrates split from the fish-amphibian lineage 450 million years ago.<\/p>
More fascinating fish facts<\/strong><\/p>