Did you know that fish can sleep with their eyes open? Yes, that’s true! Fishes don’t have eyelids, so they can’t close their eyes while sleeping. Instead, they enter a state of “resting” or “slumbering,” where they remain relatively motionless with their eyes open.
Some species of fish have developed the ability to keep one eye open while the other sleeps, allowing them to remain vigilant and keep an eye out for potential predators or prey. Imagine if you could sleep with one eye open?
But that’s not all. Some species of fishes, such as sharks and some bony fishes, need to keep moving even when they sleep to maintain a steady flow of water over their gills, which is essential for their survival. Imagine swimming while you sleep!
And did you know that some fishes can actually change color while they sleep?
The sandperch, for example, will change from a bright color to a dull, sandy color while it sleeps on the ocean floor, helping it blend in with its surroundings and avoid being spotted by predators.
What is unihemispheric sleep?
What’s more fascinating is that researchers have discovered that some fishes can exhibit a unique type of sleep called “unihemispheric sleep.” This means that one half of their brain is asleep while the other half is awake, allowing them to continue swimming and monitoring their surroundings while still getting some rest.
So, the next time you’re at the aquarium, take a moment to observe how they sleep!