John Williams, age 10, of Duluth, Minnesota, for his question:

Do fish close their eyes when they go to sleep?

We close our eyes when we shut down our movable eyelids. A fish cannot do this because he has no movable eyelids. His eyelids are as clear as glass and they are sealed in place so that he cannot open them or close them. This is why he seems to gaze around at his watery world with a fishy stare    that never even blinks.

So we know that he cannot close his eyes when he takes a nap. For this reason, it is hard to tell whether a fish is sound asleep, taking a nap or wide awake and just quietly waiting. Some fish nestle under rocks, others rest on the bottom or lie on their sides when they go to sleep. But none of them close their eyes because they cannot move their glassy eyelids.