@pamish 20 March 2021 more from that month

Do fish sleep? The dictionary defines sleep as a recurrent period of rest in which the nervous system is inactive, the eyes closed. Most fish don't have eyelids (except for sharks). Also, a great many fish live nearly motionless lives. But most fish rest. Some float in place, some wedge themselves into a spot in the mud or the coral, some even build themselves a nest. They are still alert for danger, but they are also "sleeping.