Do Fish have Eyelids?

0:00Hey 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 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 disease. 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. Whoa. Do you have any pets that love to sleep? My cat. Mew. Sleeps around 15 hours a day. Of course, for pets like dogs, cats, rabbits, birds and lizards, sleeping comes pretty easily.

1:03They 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 nest to sleep in or on. And before you know it, it's nighty night. But what about sharks? Dolphins or even just your pet goldfish? How to creatures who live in water, sleep or do they? It's time for another whiff of science on... Who's smart, Ed? Who's smart, Ed? Who smart is it you? Is it me? Is it science? Or history? Listen up. Everyone. We make smart-ing lots of fun on those smart-ed. Hey, smart-y pants.

2:08In 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. Hey Irene, swim to the shipwreck with me. There's something you gotta see. Oh yeah? What is it, Ernie? You'll see. Come. Um, see that hole in the side of the boat? Yeah? There's something in there. Take a look. Whoa. It's like a huge snake. What is it? Um, it's a moray eel. Are you trying to get us eaten? We gotta get out of here. Um, relax. It's sleeping. Sleeping? Their eyes are wide open. It's staring right at us. Shh. Shh. You awake him. I'm telling you. They're not asleep. And I'm telling you, they are.

3:08Not. Are. Now, Raider, can you decide this argument for us? Sure. So, what do you think, smart-y pants? 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? Oh, we'll last month. We learned in school that a majority of eels are nocturnal. Oh yeah, that's right. I remember. Smarty pants, do you know what nocturnal means? Irene? It means an animal that sleeps during the day and hunts for food at night. Moray eels, or more any day, 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. Whoa.

4:08So, when they sleep during the day, usually wedged between rocks or coral reefs, their eyes appear to be wide open. But what about fish? To fish, sleep, earning? Yes, of course, fish, sleep, just not in the way people in land animals do. For fish, it's more like short periods of rest than a long slumber. Some fish float in place, others wedges themselves into mud or coral, and some even find a suitable nest. And just like people, sleep helps fish recharge. What about sharks? I heard they never sleep because they have to keep moving. Well, actually, many fish need to move while sleeping to keep water passing through their gills, even if it's just a little movement. Ah. 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. Whenever method a particular shark uses to breathe, they're able to do it during periods of deep rest

5:11while remaining fairly still. Ah. And nurse sharks can be completely still while sleeping. Ooh, tell them about the parrot fish. I had a parrot fish friend, and he sleeps so weird. Ah, yes. When it's time for the parrot fish to go to sleep, it oozes out a jelly-like substance made of mucous and surrounds itself with it like a sleeping bag. This sleeping bag protects it from predators. Gross. And awesome. 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.

6:14Huh? 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. Whoa. Fun fact, it's the opposite eye from whichever half of their brain shuts down. So if their left brain shuts down, they're right high closes. At the same time, the other half of their brain and the opposite eye remain wide open and wide awake. Ah. 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. Why don't they just sleep at the surface? 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

7:15who can breathe involuntarily while we're sleeping, dolphins, purposes, and whales need to remain conscious to breathe. Ah. That's not all. After about two hours, it's the other side's turn to get some shut eye, literally. Oh. This method is known as Unihemospheric Sleep. Huh? 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. Bye, trusty narrator. OK, smarty pants. Can you guess where I am now?

8:15Did 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. 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. 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. Wow, it's pretty dark in here. And it sounds like a cave. I'll get the lights. Wow, that tanks humongous. It's also super quiet in here when I'm not talking, that is. Yeah, but kind of has to be. I'm researching the sleeping habits of various types of. Wait, let's see if the smarty pants can guess

9:17what type of sea creature you're researching. Ready, smarty pants? 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. 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. And they also share a name with a yummy food that you spread on a sandwich with peanut butter. Did you say a jellyfish? That's right. And do you want to know what's probably the most interesting thing about jellyfish? I do. What do you say, smarty pants? Yeah, they want to know too. It's a no-brainer. Oh, it's something obvious. I don't know. No, I'm saying the jellyfish is a no-brainer, because it has no brain.

10:19Wait, seriously? 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. Oh, that's old. 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. Whoa. So if a jellyfish doesn't have a brain or a central nervous system, do they sleep? Good question. 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 IXL. It's the award-winning online learning platform that fits seamlessly into your homeschool routine, covering math, language arts, science,

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12:28As 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? We've been conducting tests on a particular species of jelly known as Cassiopeia, or the upside down jellyfish. Basically, we've been using very stimuli, like lights, sounds, and physical objects to disrupt them during what appears to be their resting period. I see. So what happens? 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. I know the feeling. Exactly. So even though jellyfish lacks 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.

13:29Amazing. Got any other cool sea creature sleeping habits? I sure do. Wall vases have an air sac on their net that inflates when they sleep to keep their face out of the water and allowing them to float. Ooh, like pool floaties. Exactly. Sea horses 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. Oh. Sea stars use suckers on their arms to stick to rocks when they sleep and octopuses have two kinds of sleep. Quiet and active, huh? During quiet sleep, they lay motionless. During active sleep, they may change color and their eyes flicker around. Cool. But what about my goldfish, mango? Does she sleep in her fish tank at home? She sure does. Like all fish, goldfish do not lie down when they sleep.

14:30Rather, 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. Same here, except I prefer my bed and my pillow, which is covered in cat hair. Mew. A splashy shot out to Hudson and Sawyer in Sheralds, 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, invoiced by Brandon Bayless, Gia Davis, Jenna Hobin, and Jerry Colbert. Technical Direction and Sound Design by Josh Hahn. Who smarted is recorded and mixed

15:31at the Relic Room Studios. Our associate producer is Max Daydream Kamaski. The theme song is by Brian Suarez, lyrics written and performed by Adam Textavis. Who smarted was created and produced by Adam Textavis and Jerry Colbert. This has been an atomic entertainment production. Who smarted was created and mixed