Fishy Facts: Uncovering Underwater Breathing

Disclosure: this post contains affiliate links, which means I may receive a commission if you click a link and purchase something at no extra cost to you. Please check out our policies page for more details.

The process of fish getting the oxygen they need to breathe is so fascinating! Fish, like most other living creatures, need oxygen to extract energy from the food they eat.

But have you ever wondered how they get their oxygen?

Fish breathe through small slits called gills. Their gills are responsible for extracting oxygen from the water so their bodies can metabolize their food and have energy. This experiment provides a demonstration as to how oxygen is extracted from the water through the fish’s gills.

Time to make your best fishy face and start learning about them!

How to make the Fishy Facts Underwater Breathing experiment

Supplies you will need

For this experiment, you’ll need:

Glass cup or bowl
Coffee filter
Duct tape
Water
Sand
This FREE printable
Cardboard

Here is a very informative book about fish written for kids to accompany this experiment.

Before you start

Before you do this experiment with your child, it may be helpful to watch a short video with a visual on how fish breathe underwater. Then, come back to the experiment to watch it in action!

Instructions

Here is how to do this experiment with your child:

Step 1: Make the fish body

Head up to the Supplies section and print out the free printable I have for you. It’s a fish body printable with the fish’s gills on the side. In our house, having a visual of not only how the fish gets its oxygen, but also where on the fish this transfer occurs is a huge help!

Cut out the printable and cut a piece of cardboard to match the fish’s body. Glue them together to make our fish.

Step 2: Cut a slit in one of the gills

Next, we want to create the fish’s gills. This is the piece of the fish’s body that allows the fish to breathe underwater.

Cut a slit in one of the gills on your fish. Be sure to cut all the way through the cardboard. The slit should be big enough to fit your coffee filter.

If you want to make your fish waterproof to use multiple times, add some duct tape around the gill opening. This will keep the water off of the paper and cardboard so you can repeat the experiment.

Step 3: Create your “water”

Combine the sand and water and talk about what the sand represents (oxygen).

This is a great opportunity to talk about what makes up water (hydrogen and oxygen) and what the fish must extract in order to survive (the oxygen). Head to the STEM behind section below to see why we need oxygen to survive.

Step 4: Pour the liquid through the coffee filter and observe!

Place the coffee filter into the gill slit (you may need to fold the coffee filter to fit it in).

Hold the fish and coffee filter over a bowl or glass, then pour the sandy water through the coffee filter and observe.

If the coffee filter gets too heavy, it could fall through the fish, so be sure to hold onto the flaps.

What did the coffee filter catch? (The sand, or “oxygen”).

Coffee filter (folded) in the gill opening

Pouring sandy water in the coffee filter

Underside of the fish, showing sand/dirt staying in the coffee filter and water dripping into bowl

The STEM behind the Fishy Facts Underwater Breathing experiment

This experiment teaches:

How living beings breathe
How fish can breathe underwater
Close observation

How it works

This experiment demonstrates how fish can gather the oxygen they need through their gills to metabolize food.

The printout shows the location of the fish’s gills on the side of its body. The coffee filter represents the tiny, thin sheets that make up the gills.

As water is drawn into the fish’s mouth, it flows across the gills, collecting oxygen molecules from the water. That oxygen passes into the fish’s bloodstream through blood vessels. In our experiment, the coffee filters catch the sand, representing oxygen.

How living beings breathe

Just about all living beings need oxygen to live.

Why?

Oxygen allows our cells to break down food to get the energy needed to survive.

Mammals, reptiles, and birds all breathe in that oxygen using their lungs. Most amphibians breathe through their lungs and their skin. Fish, the last animal class, gather oxygen using their gills.

When living beings breathe in air, there is a process of extracting the oxygen that takes place. It looks a little different for each animal class, but since we’re talking about fish today, let’s explore that class!

How fish can breathe underwater

Fish use their gills to help them extract oxygen from the water. Their gills are located on the sides of their heads and have a lot of small blood vessels (capillaries).

When the fish opens its mouth and water flows in, the gills pull oxygen from the water and that oxygen is delivered to the capillaries. From there, the oxygen flows through the fish’s bloodstream.

In this experiment, we essentially create one functioning gill on our play fish. In reality, fish have several gill slits that all work to provide oxygen to the fish’s body.

Close observation

When we start pouring the sandy water through the coffee filter, we have to look closely at what is happening and be able to tie it back to how gills work underwater. This requires your child to watch the experiment closely and pay attention to the lesson, which are important lessons in themselves!