If you’re ever around a fish tank or aquarium, you may notice that the fish will stop moving for long periods of time. It might look as though they’re in a trance, but they’re actually sleeping. Generally, they rest during the day and are active at night.
Researchers have not been able to measure the familiar brain wave patterns that characterize human sleep in most fish, so they’re often referred to as “rest.” However, they do slow down their metabolic processes and physical activity, with some fish floating in place or huddled near a rock or coral reef. They also enter a state of suspended animation known as estivation during droughts and other natural disasters.
Like humans, they need rest to function properly. Their sleep cycles are based on their environmental conditions, such as available food and light levels. For instance, coral reef fish are more likely to sleep at night when they have less access to food during the day.
The most important part of a fish’s sleeping process is the emergence from the deepest level of sleep, called unihemispheric sleep. During this period, only half of their brain goes to sleep. The other half remains awake, allowing the fish to continue swimming. The eyes connected to the sleeping side of their brain remain open, a trait shared with some birds and mammals, but it doesn’t allow them to see when predators are close by.
Whether they’re sleeping or not, fish are interesting creatures. Read on for some fun jokes about fish.