(phone ringing) - Hi Doug.
- Hey Felipe. - I have a question
for you, do fish sleep? - Oh, that's a great question. It's such a great question, right? People sleep and I'm sure you've noticed lots of pets and other
animals sleeping too. Dogs sleep. Cats sleep, they sleep a lot actually. Hamsters sleep. Birds sleep. Even lizards close their eyes and sleep. But fish, I mean you probably never saw a fish sleeping did you? It's not like you see a pet fish go snuggle into a little fish
bed at the bottom of it's tank and rest it's head on
a little fish pillow. In fact, fish don't even have eyelids. I think that's what makes
this especially interesting. How would we even know
if a fish is sleeping? Like, say you had a fish
tank there in front of you, what would you look for
to try to figure out whether a fish ever sleeps? Now would be a good time to
pause the video and discuss. Okay, you ready? See with a dog or a cat not only do they lay there with their eyes shut just like we do when we sleep, but you can even sometimes see them moving their legs in their
sleep as if they're running. It seems pretty clear that dogs and cats not only sleep like we
do, but they probably even have dreams like we do. Fish do none of these things. In fact, many people who keep fish as pets will tell you, the best you
can tell with most pet fish is that sometimes the fish seem to stop swimming all over their tank. They just kind of float there for a bit, not moving much at all. Maybe that's when they're sleeping or maybe that's more like
they're taking a quick nap? The truth is, if fish do sleep it's not something that's
really obvious to us the way that it's obvious
that dogs or cats sleep. There are some kinds of fish that move constantly their whole lives. Most fish that live in
big schools do this. Day or night, these
fish are always swimming and they never take a break. Scientists think that these fish might never sleep their entire lives. Think about that, can you imagine what it would be like to always
move around and never sleep? Now that said, there are
certain other kinds of fish like many fish that live in a coal reef these fish go into little
hiding places at night and they stop moving
once they're in there. And there's other fish that even dig into the sand like this at
night time and stay there. Scientists have discovered that some fish like the bluehead wrasse,
when it's hiding at night, won't even react when a scientist nearly lifts it out of the water. It's as if these fish are in some kind of trance at night time
where they're not paying any attention to what's
going on around them. That sounds an awful lot like sleep. So, maybe some kinds of fish do sleep. If it seems like this question doesn't have one simple answer, that's because we actually don't even have one simple
idea of what sleep is. With our own bodies we know that sleep is something really important for us. If we don't go into a
nice deep sleep each night we start to become forgetful. We even have trouble thinking. If a person goes too long without sleep they might even fall
over until they do sleep. Fish don't seem to need sleep at least not deep sleep,
the same way that we do. Their bodies won't start to have problems if they don't sleep. Still, that doesn't mean
fish don't sleep at all. Based on what we can observe it seems like perhaps many fish just sleep lightly. That's all for this week's question. Thanks Felipe for asking it. Now, for the next episode I
reached into my question jar and picked out three
questions submitted to me that I'm thinking about answering. When this video is done playing
you'll get to vote on one. You can chose from, why do some things stain your clothes? How are magnets made? Or, who invented pizza? So submit your vote when the video's over. I want to hear from all of you watching. There are mysteries all around us stay curious and see ya next week.
