I WONDER - Do Fish Have Eyelids?

Fish lack eyelids, so their eyes remain open even while sleeping. Unlike most animals, fish do not fully relax their brains during sleep, but they slow their breathing and movement. Sharks, on the other hand, have eyelids, but they do not close completely.

Why don't fish have eyelids?

How do fish sleep differently from most animals?

What happens to a fish's brain when it is sleeping?

In what way do fish remain alert even while sleeping?

What is the significance of a shark's eyelids?