Do fish sleep? Sort of. Here's how to catch some z's under the sea.

Sleep is one of the most essential parts of being human. Catching some Z’s is important for daily functioning. As adults, we've got to get in about eight hours a day, according to the Sleep Foundation.

The same is not true for all mammals. Some only need a few hours, like elephants at two hours per day. Giraffes sleep just under five hours a day. Bats, who are nocturnal, spend 20 hours a day sleeping, and even dogs need much more sleep than humans.

When it comes to sleep for non-mammals, the question of sleep has a different answer. If you’ve ever wondered if fish join us while we sleep — and how you can even tell when a fish is sleeping — you can find your answer here.

Do fish sleep?

Fish don’t sleep like humans, but they do rest by reducing their activity and metabolism, the National Oceanic and Atmospheric Administration (NOAA) says.

Mammals sleep when the neocortex — a part of the brain that processes sensory, motor, language, emotional and associative information — shuts down. According to Aqueon, fish lack a neocortex and eyelids to close during sleep, making their "sleep" process different from mammals'.

In 2019, Stanford University researchers found that zebrafish are one type of fish that actually sleep similarly to humans. Though they don’t have eyelids to close, they display slow-wave sleep and a type of REM sleep. Stanford researchers said this could help with sleep abnormality research in the future.

How do you know if a fish is sleeping?

While resting, fish still remain alert for danger and either float in place or burrow in a safe spot. You can tell if a fish is sleeping if they remain motionless for a bit or lay at the bottom of the aquarium, according to the NOAA.

How long do fish sleep?

Research indicates fish rest on similar schedules to humans by remaining active during the day and resting at night. There are some species of fish, like catfish and knife fish, that are nocturnal, Aqueon says. There’s also evidence fish don’t sleep during every phase of their life. Most fish don’t sleep when they’re caring for their young, migrating or some even until they’re several months old.

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This article originally appeared on USA TODAY: Do fish sleep? How to tell if your pet is getting some shut eye