Do Fish Sleep?

Many of us have had a pet fish at some point in our lives, and it's hard to tell when they're sleeping since they don't have eyelids. But scientists know that fish do rest and some have very interesting ways of doing it.

Fish don't sleep the same way that you or your dog or any other mammal does. Most don't seem to experience cycles of rapid eye movement or REM, though to be fair, we might just not know how to recognize dream state activity in these animals. For example, research on zebrafish suggests that they experience similar brain activity to REM sleep, and other researchers have observed an octopus changing colors while sleeping, which may suggest that it was dreaming.

Still, scientists have observed that many species of fish rest. This is a period of restoration when their metabolic functions slow and they're less active. Some fish like reef sharks lay still at the bottom of the ocean or inside caves when they sleep. These sharks have a unique anatomical feature called a spiracle that forces water out of the sharks gills so that they can continue to breathe while they're resting.

Other species of sharks and tuna must keep swimming to breathe because they don't have SPs to keep water flowing over their gills. In their cases, scientists hypothesize that they shut off half of their brains, which is what dolphins do. They slow their breathing and move more slowly, but are still somewhat responsive to their environment.

But some fish species like the Spanish hogfish, are known to sleep very soundly, so soundly in fact, that divers can touch them and even move them to the surface without disturbing their slumber. Some relatively deep sleepers create their own protection. A parrotfish, for instance, create enough mucus to form a cocoon around themselves at night when they stop moving. This mucus blanket is likely used to keep blood sucking parasites from clinging to them while they sleep. And clownfish bury themselves in cnn enemies to protect themselves from predators while they sleep alike.

Humans fish have biological clocks that tell them when to be alert and awake and when to rest, and some sleep during the day and some sleep at night. These tendencies primarily evolved based on when they're more or less likely to be attacked by predators or what the best times are to find a meal.

One of the more bizarre sleeping habits of the ocean is experienced by LOEs A, which float to the top of the water and remain completely still when they sleep for short periods is soap. If your pet fish is a loach and it's motionless at the top of the tank, it could very well be sleeping. Unfortunately, the same cannot be said about that pet goldfish, which tend to rest toward the bottom of their habitat, not upside down near the surface.

It's fascinating to learn about the different ways that fish sleep, and it's a reminder that the world of animals is full of surprises. We may never know exactly what fish experience when they rest, but it's clear that they do rest and that it's an important part of their lives.