Squeaks and I are adopting a pet goldfish!

He lives in a fish tank, and he’s a great swimmer! In fact, this little guy’s whole body is really suited to life in the water.

He has great fins to help him swim, and eyes that can stay open in the water. These special body parts help him to live in his underwater home, so we call them adaptations. There’s one adaptation that’s really important for our new fish friend to survive in a fish tank or pond.

He needs to be able to breathe underwater. People can’t breathe underwater because there’s no air. We have to hold our breath, or use special equipment like scuba gear to get air.

But our goldfish isn’t holding his breath, and he didn’t bring scuba gear! Instead of breathing air, he actually breathes water. Humans, fish, and all kinds of other animals have to breathe for the same reason: we all need something called oxygen.

Even though air might not seem like it's made of anything, it's actually made up of lots of tiny things called molecules that are way too small for you to see. Oxygen is one of the ingredients in air, and it's really important: it helps your body make energy! You need oxygen to break down your food, move your muscles, and even just to think with your brain.

There's oxygen in air, but you need it to get into and all around your whole body! So, you have special organs called lungs to help get that oxygen. When you breathe in, you can feel your lungs expand full of air, just like a balloon.

Once they’re full of air, your lungs pull the oxygen that you need out of the air before you breathe out. That oxygen goes into your blood and travels all throughout your body. There’s air all around us, so as long as you we breathe, you can get oxygen.

Land animals can have all different shapes and sizes of lungs, but animals that live underwater, like fish, need oxygen, too! Fish don’t have lungs, and there isn’t any air around them. Animals like our goldfish need to use another way to get their oxygen.

And guess what? Water is full of oxygen, just like the air is! So fish can get their oxygen straight from the water they live in.

They just need an adaptation to get the oxygen out of the water. Instead of lungs, most underwater creatures have another special body part that allows them to pull oxygen straight out of the water, called their gills. Gills look like little slits on either side of a fish’s face.

A fish’s gills work a lot like our lungs. When a fish pulls in water through its mouth, the water goes back out through its gills. As the water runs through the gills, it goes right past the fish’s blood.

The oxygen in the water flows into the fish’s blood, and now the fish can use the oxygen all over its body! The fish is basically breathing water with gills, instead of air with lungs. Other types of animals besides fish use gills, too.

Crabs, lobsters, snails, and even some bugs use gills to breathe! So, even though we both have very different ways of getting it, our goldfish needs oxygen just like I do. Isn’t that right, little fish?

What do you think we should name our new fish? Ask a grown-up to help you leave a comment below, or you can send us an email at kids@scishow.com Thanks, and we'll see you next time here at the Fort!