Fish can sleep, and the amount of sleep they need depends on many factors, such as the degree of light and the amount of previous activity.
However, when the fish is sleeping, it may not seem obvious. First of all, the fish have no eyelids, so when they are sleeping, the eyes still look open; the fish will not experience a rapid eye movement sleep period – the unique sleep stage of the baboons.
Although many people question whether fish really sleep, their state of sacredness is proof of sleeping. When the fish sleep, they will stay at the bottom of the habitat, and some will even swim while sleeping.