How Do Fish Sleep?

Many have questioned whether fish do even sleep, because they don’t have eyelids and therefore can’t close their eyes or experience rapid eye movement (REM). However, scientists have now studied behavioural patterns that suggest fish do sleep, but look more like they are daydreaming.


Some species of shark must constantly swim to ventilate their gills, even as they sleep.

Fish don’t lie down, but tend to settle towards the bottom of their watery habitats. Some even need to keep moving while they doze to ensure constant ventilation of their gills. The amount of shuteye a fish gets depends on how active it has been, as well as various environmental factors. Interestingly, they can also suffer from sleep disorders and deprivation. So although fish sleep in a different way to us, there are some similarities.