The quick answer
Fish need oxygen, just like us. There is a little oxygen mixed into water. Fish take in water through their mouth and push it out over their gills. The gills catch the oxygen and pass it into the blood.
RankiTanki, if I dive under water, I have to come up for air really soon. How do fish stay down all day?
TankiFish breathe too, just in a different way. Their secret tool is called gills.
Everybody needs oxygen
All animals need a gas called to live. We get it from the air. When we breathe in, our take oxygen out of the air and pass it into our blood.
Water has oxygen too. You cannot see it, but tiny amounts of it are mixed into the water. Waves, wind and water plants help put it there. Fish are experts at getting it back out.
Gills do the job
Instead of lungs, fish have . They sit on both sides of the head. In many fish, you can see a flap that covers them. It opens and closes as the fish breathes.
Gills look a bit like red feathers, or the pages of a tiny book. They have lots of thin parts packed close together. Inside these parts are tiny tubes full of blood. These tubes are called .
How a fish breathes, step by step
- The fish opens its mouth and lets water flow in.
- It closes its mouth and pushes the water back over its gills.
- The gills catch the oxygen from the water.
- The oxygen moves into the blood and travels all around the body.
- The used water flows out through openings on the sides of the head.
Gills are red because they are so full of blood. Their thin, feathery parts give the water lots of places to touch. That way, the fish can catch as much oxygen as possible.
RankiSo can a fish breathe air if it jumps out of the water?
TankiMost fish cannot. Out of water, the thin parts of their gills stick together and stop working.
Sharks, whales and dolphins
Some sharks have to keep swimming to breathe. As they swim, water rushes into their open mouth and over their gills. Great white sharks and whale sharks breathe like this. Many other sharks can rest on the sea floor and still pump water over their gills.
Whales and dolphins live in water, but they are not fish. They are , like us. They have lungs and must swim up to the surface to breathe air. They breathe through a hole on top of their head, called a .
Try it
Count a fish’s breaths
You need
What to do
- Find a fish in a fish tank or a pond. Go with a grown-up.
- Watch the flaps on the side of its head open and close.
- Count how many times they open in one minute. Write down your number.
- Watch a different fish and count again. Which one breathes faster?
- Do not tap on the glass or put your hands in the water.
Ask a grown-up to help you with this one.
RankiSo fish do not hold their breath at all. They take oxygen from the water with their gills.
TankiExactly. Gills for fish, lungs for us and a blowhole for whales. Everyone has their own way to breathe!
Big words
- oxygen
- A gas in air and water that animals need to live.
- gills
- The parts of a fish that take oxygen out of the water.
- lungs
- The two soft bags in your chest that fill with air when you breathe.
- blood vessels
- Tiny tubes that carry blood all around the body.
- mammals
- Animals that breathe air and feed their babies with milk.
- blowhole
- The nose hole on top of a whale’s or dolphin’s head.
Quick quiz
1. What gas do fish need to live?
Fish need oxygen, just like we do. They take it from the water.
2. How do dolphins breathe?
Dolphins are mammals. They swim up and breathe air through their blowhole.
3. What do fish use to catch oxygen from the water?
Gills are full of tiny blood vessels that take oxygen from the water.
For parents and teachers
Gills work because oxygen passes from the water into the blood across very thin membranes. In many fish, blood flows in the opposite direction to the water, which makes this exchange very efficient. A visit to an aquarium is a good chance to compare how different animals breathe, from fish to turtles and seals.
Pictures marked “AI generated” were made with AI tools. Ranki and Tanki are AI generated characters. Found a mistake? Write to info@pr-geo.com and we will fix it.
