How Do Fish Breathe Underwater? It’s Science!

If you find yourself at a beach, lake or aquarium this summer, chances are you’ll hear a child ask, “How do fish breathe underwater, and why can’t people?” Curious kids have been pondering this question for ages. Luckily, the answer is simply science! Keep reading to discover how many fish, dolphins, whales and even sea stars can thrive in an aquatic environment.

Fish

Most fish have special organs called gills that allow them to breathe oxygen by extracting it from water. Fish take in water through their mouth, and it passes across the gills on its way out. When it does, oxygen gets diffused into the bloodstream and travels through the fish’s body. Some fish have to keep swimming for the water to flow through their gills while others can swallow water and push it through on their own.

Help your child research their pet fish or any favorite fish to see how they use their gills!

Dolphins and Whales

Dolphins and whales are mammals – even though they spend their lives in the water. Because of this, they don’t breathe underwater like fish do. Dolphins and whales have lungs to breathe air. To help them go for longer periods of time before needing to surface for air, these mammals can store oxygen in their muscles and blood. When it is time to come up for a breath, they use the blowhole on the tops of their heads – just like we use our nose to breathe.

Ask your child what they would explore if they could hold their breath underwater for as long as a dolphin or a whale can.

Sea Stars

While often referred to as starfish, these creatures actually are not fish at all! Sea stars do not rely on gills to extract oxygen from the water, but they do still require oxygen to survive like most living creatures. Instead, sea stars have a water vascular system that helps them breathe effectively underwater. Using the hair-like spikes called papulae that are all over their backs, sea stars expand their surface area to gather oxygen from the water through diffusion. Then they use sea water to circulate that oxygen throughout their body.

What other unique creatures, either underwater or on land, would your child like to investigate?

Learn More

Encourage your child to stay curious about the world around them and check out our blog to uncover more examples of real-life STEM to share.