Fish do not have eyelids. They need dark to sleep. Homes have lights on a lot at night before e go to sleep. I even have one tank which I cover with a big towel each night. However, let's not forget those fish that are active at night and tend to sleep in caves/hidey holes during the day. So there is the day shift and the night shift ?
Usually, the day shift hides from the night shift. It helps to prevent waking up in somebody's stomach......