Do Fish have Eyelids?

Summary

Podcast Summary: Who Smarted? – "Do Fish have Eyelids?"

Date: March 23, 2026
Podcast by: Atomic Entertainment / Starglow Media
Theme: Do Fish Have Eyelids? The Sleepy Secrets of Underwater Creatures

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Episode Overview

This lively episode dives underwater to explore an unusual question: Do fish have eyelids? Along the way, the Who Smarted? crew uncovers how various sea creatures handle sleep, busting myths and sharing weird, wonderful adaptations—from jellyfish "sleeping" without a brain to dolphins half-awake with one eye open. The episode masterfully blends fun banter with sharp facts, making science about the ocean's sleepers both hilarious and memorable for curious young listeners and their families.

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Key Discussion Points & Insights

1. Setting the Scene: How Do Underwater Animals Sleep?

• Narrator introduces the topic by relating human and pet sleep needs to the mysterious world of marine animals.

  “But what about sharks, whales, dolphins, or even just your pet goldfish? How do creatures who live in water sleep? Or do they?” (01:16)

• Transition from human habits to the enigmatic sleep routines under the sea.

2. Do Fish Have Eyelids? (And Are They Sleeping?)

• Fish do not have eyelids, so when seen resting with open eyes, they’re often still sleeping.

  “Just like fish, they don’t have eyelids. So when they sleep during the day, their eyes appear to be wide open.” (04:07)

• Moray eels and other nocturnal species may look awake but are often resting.
  Memorable Moment:

  ERNIE: “You awake him.”
  IRENE: “I’m telling you, they’re not asleep.”
  (03:00)

3. Unique Sleeping Styles of Fish

• Fish sleep in short rest periods rather than one long stretch.
• Sleep adaptations:
  • “Some fish float in place, others wedge themselves into mud or coral, and some even find a suitable nest.” (04:26)
• Sharks: Contrary to the myth, some can rest while hardly moving; nurse sharks can be completely still while sleeping.

  “Whatever method a particular shark uses to breathe, they’re able to do it during periods of deep rest while remaining fairly still.” (05:02)

  • Parrotfish uniquely protect themselves by encasing in a mucus sleeping bag at bedtime.

    “This sleeping bag protects it from predators.” (05:24)

4. Sea Mammals: Sleeping with One Eye Open

• Dolphins and whales demonstrate unihemispheric slow-wave sleep: half their brain sleeps at a time, with one eye open.

  “When a whale or dolphin goes to sleep, only half their brain shuts down and only one eye closes.” (06:15)

• This adaptation helps them remain partially alert for predators and enables them to surface for air.

  “It’s the opposite eye from whichever half of their brain shuts down… This allows them to literally keep an eye out for predators.” (06:25)

• They alternate brain sides every two hours and clock ~8 hours of sleep daily.

  “This method is known as unihemispheric sleep.” (07:33)

5. Behind the Scenes: A Marine Biologist Explains

• Becky, the marine biologist, provides hands-on insights from her research.
  • Describes quiet observation settings and hints at unique sea creatures (jellyfish!) who sleep in strange ways.

    “What sea creature can glow in the dark, use its tentacles to sting its prey... and can be found in both freezing Arctic oceans and tropical seas?” (09:14)

  • Jellyfish: No central brain or nervous system; survived since before dinosaurs.

    “No, I’m saying the jellyfish is a ‘no brainer’ because it has no brain.” (10:10)

    • Even without a central nervous system, jellyfish exhibit rest cycles. If disrupted, they’re “slower to respond to things the next day.” (13:00)

6. More Marvelous Marine Sleep Tricks

• Walruses: Inflate air sacs in their necks to float and keep their faces out of water while sleeping.

  “Walruses have an air sac on their neck that inflates... allowing them to float.” (13:32)

• Seahorses: Curl their tails around plants or coral to anchor themselves mid-slumber.
• Baby sea otters: Hold hands with their moms so they don’t drift apart while sleeping.
• Sea stars: Use arm suckers to cling to rocks as they sleep.
• Octopuses: Experience both ‘quiet’ and ‘active’ sleep phases, including changing color and eye movements.

  “During active sleep, they may change color and their eyes flicker around.” (14:11)

7. Goldfish: Sleepy Pet Facts

• Goldfish rest by hovering in place, usually head down, in dark and quiet environments at home.

  “Like all fish, goldfish do not lie down when they sleep. Rather, they become less active… Goldfish sleep about eight to twelve hours every day, usually when it’s dark and quiet.” (14:24)

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Notable Quotes & Memorable Moments with Timestamps

• “Just like fish, they don’t have eyelids. So when they sleep during the day... their eyes appear to be wide open.” — Narrator (04:07)
• “I’m telling you, they’re not asleep.” — Irene (03:02)
• “Whatever method a particular shark uses to breathe, they’re able to do it during periods of deep rest while remaining fairly still.” — Narrator (05:02)
• “This sleeping bag protects [parrotfish] from predators.” — Narrator (05:24)
• “When a whale or dolphin goes to sleep, only half their brain shuts down and only one eye closes.” — Narrator (06:15)
• “The jellyfish is a no brainer because it has no brain.” — Becky (10:10)
• “Even though jellyfish lack some of the essential organs and systems... they too need to catch some Z’s.” — Becky (13:14)
• “Walruses have an air sac on their neck that inflates when they sleep to keep their face out of the water and allowing them to float.” — Becky (13:32)
• “Baby sea otters hold hands with their mommies to keep from floating away when they sleep.” — Becky (13:45)

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Important Segments & Timestamps

| Timestamp | Segment Description | |-----------|-----------------------------| | 00:02 | How do animals (including fish and sea creatures) sleep? | | 02:20 | Introduction of moray eel and nocturnal animal sleep | | 04:07 | Fish have no eyelids—yet they sleep! | | 05:17 | Parrotfish “sleeping bag” adaptation | | 06:15 | Dolphins and whales' unihemispheric sleep explained | | 09:14 | Marine biologist Becky introduces jellyfish and brainless sleep | | 13:00 | Jellyfish rest, sluggishness when sleep deprived | | 13:32 | More fascinating aquatic sleep tactics (walrus, seahorse, otter, starfish, octopus) | | 14:24 | Goldfish sleep facts for pet owners |

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Episode Takeaways

• Fish and many sea creatures DO sleep, but their methods are often wildly different (and cooler) than ours—ranging from “eyes wide open” resting to half-brain alertness and even sleeping in floating “mucus sleeping bags.”
• Notably, no, fish do not have eyelids!
• Sea mammals, jellyfish, sharks, and even cute otters all showcase remarkable adaptability.
• Kids (and adults) will likely run to their fish tank or local aquarium to look for "sleeping" fish in action after hearing these fun facts!

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Overall Tone

The episode is playful, curious, and slightly goofy, with every fun fact delivered in a way that’s both scientifically accurate and laugh-worthy—making marine biology totally splashy for kids and parents alike.

Transcript

[Narrator]

Hey there, smarty pants. Quick question. What's the last thing you do every night? I mean, the very last thing? Here's a hint. Usually it involves a bed and a pillow. Sometimes it comes after some light reading or listening to your favorite podcast. Did you say go to sleep? Yep. When it comes to improving your overall mental and physical health as. As well as increasing your attention, behavior and memory, few things are as important or good for you as sleep. Trust me, I am all about the Zs. But humans aren't the only ones who benefit from lots and lots of sleep. Animals need sleep, too. And some need even more sleep than humans.

[Ernie]

Whoa.

[Narrator]

Do you have any pets that love to sleep? My cat, meow, sleeps around 15 hours a day. Of course, for pets like dogs, cats, rabbits, birds and lizards, sleeping comes pretty easily. They have beds, cages, or tanks to curl up in. Or if you're my cat, my pillow. Same goes for any land animal, really. Just find a nice comfy patch of ground grass or a nest to sleep in or on, and before you know it, it's nighty night. But what about sharks, whales, dolphins, or even just your pet goldfish? How do creatures who live in water sleep? Or do they? It's time for another whiff of science on the smart egg. Who smarted? Who's smart? Is it you? Is it me? Is it science? Or history? Listen up, everyone. We make smarting lots of fun, but who's smart? And. Hey, smarty pants, in case you couldn't tell, I'm scuba diving in the ocean. It's a lovely afternoon, and in just a moment, school's about to let out a school of fish, that is. Listen.

[Ernie]

Hey, Irene, swim to the shipwreck with me. There's something you gotta see.

[Irene]

Oh, yeah? What is it, Ernie?

[Ernie]

You'll see. Come see that hole in the side of the boat?

[Irene]

Yeah, there's something in there.

[Narrator]

Take a look.

[Irene]

Whoa. It's like a huge snake. What is it?

[Ernie]

It's a moray eel.

[Irene]

Are you trying to get us eaten? We gotta get out of here.

[Ernie]

Um, relax. It's sleeping.

[Irene]

Sleeping? Their eyes are wide open. It's staring right at us.

[Ernie]

You awake him.

[Irene]

I'm telling you, they're not asleep.

[Ernie]

And I'm telling you they are not are. Narrator. Can you decide this argument for us?

[Narrator]

Sure. So what do you think, smartypants? Should these fish be worried about this moray eel? Remember earlier I said it was a lovely afternoon? What do we know about moray eels that could make them less of a threat during the day? Ooh.

[Ernie]

Well, last Month we learned in school that a majority of eels are nocturnal.

[Irene]

Oh yeah, that's right. I remember, smartypants.

[Narrator]

Do you know what nocturnal means, Irene?

[Irene]

It means an animal that sleeps during the day and hunts for food at night.

[Narrator]

Moray eels, or Moranidae, are a family of eels who can be found all over the world. There are over 200 known species of moray eels that fall into two categories based on where the fins appear along their slithery snake like body. And guess what? Just like fish, they don't have eyelids.

[Irene]

Whoa.

[Narrator]

So when they sleep during the day, usually wedged between rocks or coral reefs, their eyes appear to be wide open. But what about fish? Do fish sleep? Ernie?

[Ernie]

Yes, of course fish sleep, just not in the way people and land animals do.

[Narrator]

For fish, it's more like short periods of rest than a long slumber. Some fish float in place, others wedge themselves into mud or coral, and some even find a suitable nest. And just like people, sleep helps fish recharge.

[Irene]

What about sharks? I heard they never sleep because they

[Becky]

have to keep moving.

[Narrator]

Well, actually, many fish need to move while sleeping to keep water passing through their gills, even if it's just a little movement. As for sharks, it's often repeated that sharks never sleep because they have to keep moving to stay alive. But is it true? Nope. Whatever method a particular shark uses to breathe, they're able to do it during periods of deep rest while remaining fairly still. And nurse sharks can be completely still while sleeping.

[Ernie]

Ooh, tell them about the parrot fish. I had a parrot fish friend and he slept, so. Oh, weird.

[Narrator]

Ah, yes. When it's time for the parrotfish to go to sleep, it oozes out a jelly like substance made of mucus and surrounds itself with it like a sleeping bag. This sleeping bag protects it from predators.

[Irene]

Gross and awesome.

[Narrator]

Now you might be thinking, of course fish can sleep in the ocean, but what about sea mammals who can't breathe water and have to rise to the surface for air? Creatures like whales and dolphins, do they sleep? Smarty pants? Do whales and dolphins A, take a huge breath and sleep only as long as the breath lasts, B sleep with one eye closed, or C, not sleep at all? If you said B, sleep with one eye closed, you're right.

[Irene]

Huh?

[Narrator]

It might sound totally crazy, but when a whale or dolphin goes to sleep, only half their brain shuts down and only one eye closes.

[Irene]

Whoa.

[Narrator]

Fun fact. It's the opposite eye from whichever half of their brain shuts down. So if their left brain shuts down, their right eye closes at the same time. The other half of their brain and the opposite eye remain wide open and wide awake.

[Irene]

Ah.

[Narrator]

This allows them to literally keep an eye out for predators and helps them avoid swimming into things. This method also acts like a clock, so they know when it's time to swim up to the surface and take in some much needed air.

[Irene]

Why don't they just sleep at the surface?

[Narrator]

Good question. Whales and dolphins often do swim at or near the surface. But guess what? They still need to sleep like this. Because unlike humans, who can breathe involuntarily while we're sleeping, dolphins, porpoises, and whales need to remain conscious to breathe. That's not all. After about two hours, it's the other side's turn to get some shut eye. Literally.

[Irene]

Oh.

[Narrator]

This method is known as unihemispheric sleep.

[Irene]

Huh?

[Narrator]

This process is repeated multiple times, with these mammals averaging about eight hours of sleep over the course of a day. Now it's time to head back to land and meet a friend who knows a lot about marine animals and more specifically, how they sleep. Later, Irene. Later, Ernie.

[Irene]

Bye, trusty narrator.

[Narrator]

Okay, smarty pants, can you guess where I am now? Did you say an aquarium? As you might know, an aquarium is an amazing place to safely observe marine life up close without getting wet. Today I'm meeting my friend Becky, who happens to be a marine biologist. Hello. She studies aquatic organisms and their behaviors as they interact with the environment around them. Whoa. Ooh, I see her. Hey, Becky. Good to see you. These are my friends I told you about, the smarty pants.

[Becky]

Hello, and welcome. I've been waiting for you. Let's go learn some more about sleeping sea creatures. My research lab and observation tank are right this way.

[Narrator]

Wow, it's pretty dark in here. And it sounds like a cave.

[Becky]

I'll get the lights.

[Narrator]

Wow, that tank's humongous. It's also super quiet in here. When I'm not talking, that is.

[Becky]

Yep, it kind of has to be. I'm researching the sleeping habits of various types of.

[Narrator]

Wait. Let's see if the smarty pants can guess what type of sea creature you're researching. Ready, smarty pants? What sea creature can go glow in the dark, use its tentacles to sting its prey, and can be found in both freezing Arctic oceans and tropical seas.

[Becky]

If you're still stumped, here's another hint. Even though these sea creatures can grow quite large, you can practically see right through them.

[Narrator]

And they also share a name with a yummy food that you spread on a sandwich with peanut butter.

[Becky]

Did you say a jellyfish? That's right. And do you want to know what's probably the most interesting thing about jellyfish?

[Narrator]

I do. What do you say, smarty pants? Yeah, they want to know too.

[Becky]

It's a no brainer.

[Narrator]

Oh, it's something obvious. Um, I don't know.

[Becky]

No, I'm saying the jellyfish is a no brainer because it has no brain.

[Narrator]

Uh, wait, Seriously?

[Becky]

Seriously? Unlike most inhabitants on earth, jellyfish belong to one of the oldest animal groups and split from the others nearly 600 million years ago. They've been around since before the dinosaurs.

[Narrator]

That's old.

[Becky]

Sure is. Not only that, but they also lack a central nervous system, which truly makes them one of the furthest, evolutionarily speaking, from humans and most higher functioning animals.

[Ernie]

Whoa.

[Narrator]

So if a jellyfish doesn't have a brain or a central nervous system, do they sleep?

[Becky]

Good question.

[Narrator]

And we'll have the answer right after this quick break. Spring is here. And if you're a homeschool family trying to finish the year strong, I want to tell you about about ixl. It's the award winning online learning platform that fits seamlessly into your homeschool routine covering math, language arts, science and social studies from Pre K through 12th grade. What I love most about IXL is how it adapts to each child's pace. Whether your kid needs to reinforce foundational skills before an assessment or push ahead into new material, IXL meets them exactly where they are with no pressure and real encouragement built right in. Kids earn rewards, see their own progress, and actually feel good about learning. And for parents, the real time progress tracking is a game changer. You always know exactly where your child stands. Plus, it makes learning fun. And you know, I love that. Over 15 million students use IXL and it's proven to improve achievement in all 50 states. So. So make an impact on your child's learning. Who smarted? Listeners get an exclusive 20% [e-mail] smarted that's ixl.com smarted for your 20% off. Now back to whosmarted. As you know, sleeping is the best way to recharge your body and brain. But what happens if you don't have a brain like a jellyfish? Can you still sleep? What do you say? Becky?

[Becky]

We've been conducting tests on a particular species of jelly known as Cassiopeia, or the upside down jellyfish. Basically, we've been using various stimuli like lights, sounds and physical objects to disrupt them during what appears to be their resting period.

[Narrator]

I see. So what happens?

[Becky]

Pretty much the same that happens when other Animals, or even humans don't get enough sleep. They're not as active and are much slower to respond to things the next day.

[Narrator]

I know the feeling.

[Becky]

Exactly. So even though jellyfish lack some of the essential organs and systems that nearly all other creatures have, they too need to catch some Z's after a hard day swimming around the ocean looking for food.

[Narrator]

Amazing. Got any other cool sea creature sleeping habits?

[Becky]

I sure do. Walruses have an air sac on their neck that inflates when they sleep to keep their face out of the water and allowing them to float.

[Narrator]

Ooh, like pool floaties.

[Becky]

Exactly. Seahorses wrap their tail around coral or sea plants to keep from floating away while sleeping. Baby sea otters hold hands with their mommies to keep from floating away when they sleep. Sea stars use suckers on their arms to stick to rocks when they sleep. And octopuses have two kinds of sleep. Quiet and active.

[Irene]

Huh.

[Becky]

During quiet sleep, they lay motionless. During active sleep, they may change color and their eyes flicker around.

[Narrator]

Cool. But what about my goldfish, Mango? Does she sleep in her fish tank at home?

[Becky]

She sure does. Like all fish, goldfish do not lie down when they sleep. Rather, they become less active, staying in one place and moving slowly to keep themselves stable. They might do this near the surface or an inch or so off the bottom with their heads pointed slightly downward. Goldfish sleep about eight to 12 hours every day, usually when it's dark and quiet.

[Narrator]

Same here, except I prefer my bed and my pillow, which is covered in cat hair. Meow. A splashy shout out to Hudson and Sawyer in Sherrods, Ford, North Carolina. I hear you listen to who Smarted every night at bedtime. And Hudson. I love your big question about how orcas and other sea animals stay hydrated. Keep those curious questions coming and keep on smarting with who Smarted this episode. Sleeping Sea Creatures was written by Dave Davis and voiced by Brandon Bayless, Gia Davis, Jenna Hoban and Jerry Colbert. Technical direction and sound design by Josh Hahn. Who Smarted is recorded and mixed at the Relic Room Studios. Our associate producer is Max Daydream Kamasky. The theme song is by Brian Suarez, lyrics written and performed by Adam Tex Davis. Who Smarted was created and produced by Adam Tex Davis and Jerry Colbert. This has been an Atomic Entertainment production.