Asked by: Malgo Chrzan, London
It’s hard to say if fish sleep like we do. Most can’t close their eyes and have no neocortex, which is the part of the mammalian brain that displays distinct patterns of activity during sleep. Even so, many fish settle down for the night on the seabed.
Parrotfish sleep inside a mucous bubble, perhaps so predators can’t smell them. At night, zebrafish float in the water column and are difficult to rouse. Some fish never seem to sleep, including blind cave fish and fish swimming in shoals through featureless water. It could be they receive limited sensory input and their brains don’t need to rest.