Do Fish Sleep and How?

Not that this question has been puzzling me a lot, but I still would like to know Do fish sleep? And if yes, how? I can’t agree more, that everyone needs rest and sleep. But, I am just curious HOW?

So, I found out, that most fish do sleep, but it is not a kind of special ritual for them (I mean cleaning teeth, wearing pajamas … ) and what is more, poor fish don’t have eye-lid, so they can’t close their eyes even if they would like to.

It is important to know, that being asleep can mean various things and states to various fish. Some of them are motionless while sleeping, some rest against rocks and some sleep under a log. Sometimes fish can be active at night and rest during the day and vice versa, of course.

And one more interesting fact, sharks have to push water through their mouths ALL THE TIME, they can’t stop, otherwise, they won’t breathe and die… So, I think, they sleep, but scientists just don’t know how!