Fun fact: humans and most mammals have eyelids to keep dirt and dust out, but since fish live in water, they don't need eyelids. So fish do not sleep with their eyes closed!
Fish sleep is not exactly like human sleep. They don't have beds, sheets, blankets or pillows. In fact, some fish keep moving even when they are asleep! You can spot a fish sleeping if they seem to be hovering in place or moving slowly.
When fish rest, they keep a constant flow of water moving past their gills to maintain oxygen levels in their bodies. Like humans, fish have an internal clock that tells them when to sleep and when to eat. Fish are all different! Many catfish, eels and electric fish are nocturnal. This means they are most active at night, busy hunting for food, and rest during the day.
Scientists continue to study the sleeping habits of fish. Some fish go through a state of dormancy at certain times of the year. Dormancy is a period in a life cycle when growth and physical activity are paused. This helps save energy as a response to environmental conditions, like extreme cold or drought. During winter, some fish rest in mud if they can't migrate to warm water. Some lie motionless at the bottom of the water.
Although sleepy fish may seem like they are in a trance, most can dart away quickly if they are attacked or disturbed. Try feeding your pet goldfish while they're asleep. They may take a few seconds to realize there's food in the tank.
Speaking of tanks, here's a joke from one of our TPL Kids readers. Two fish are in a tank. One of them says, "How do you drive this thing?"