Do fish sleep ?

Have you ever wondered whether fish sleep ? Fish are so different from us, in form and environment, that perhaps at some point it has occurred to you that sleeping might be a bit tricky for them. They float in deep water, moving almost continuously, and cannot go and lie down like a land creature. They’re very vulnerable so can hardly float around unconscious in the sea. And their eyes seem to be open all the time …. It’s just difficult to envisage them sleeping (especially tucked up in bed in pyjamas).

A friend posed this question recently (Thanks to C for asking !), and a few searches on the internet provided the answer, which is: ‘yes and no and sort of’.






Fish do need deep rest, like mammals, and for this they swim to a quiet sheltered place such as underneath a rock and lie very still. And yes, brain activity decreases, but we don‘t really know if it is the same as sleep among mammals. An alternative approach adopted by some fish is to keep swimming, with one half of the brain ‘sleeping’, and then the other half. A further twist is that fish cannot close their eyes, since they have no eyelids, so their eyes are always open.





Altogether, then, fish do have some deep rest, but whether it is sleep as we know it is unclear.
All this leads to another question: do fish dream ? Now that really is something we may never know ….