Ask Tappity: Science Questions for Kids > How Do Fish Breathe?
How Do Fish Breathe?
Fish are always underwater - so how do they breathe? Watch this video to find out, or read our explanation below!
There’s Oxygen Dissolved In Water
All animals need oxygen, including fish. Humans and other land animals get oxygen from the air, which is full of it. Water also has air dissolved in it, sort of like the carbon dioxide gas dissolved in a can of soda. There isn’t as much oxygen in the water as there is in the air, but it’s still there, and fish are able to get it.
Fish Use Gills To Breathe
We get oxygen by filling our lungs with air. Once the air is against the surface of our lungs, the oxygen moves on its own from the air to our blood in a process called diffusion. Fish use a really similar process, except instead of filling lungs with air, they constantly pass water over their gills. Gills consist of thousands of individual hairlike strands, and oxygen is able to pass into the fish’s bloodstream along the entire surface of every one. Because their gills have so much surface area for water to pass over, they’re able to get enough oxygen to survive despite the relative lack of oxygen in water compared to air.
Fish Can’t Breathe Outside Water
If fish can breathe in water, and air has more oxygen than water, then shouldn’t fish be able to breathe air? The answer is no, and it’s because gills don’t work properly outside of water. If you submerge your hair in the water, it floats around, with all the hairs separating. But when you take your hair out, it all collapses together, weighed down and glued together by the water. The same thing happens to gills - when you take a fish out of the water, the strands of the gills collapse, getting rid of all that valuable surface area that’s necessary for enough oxygen to diffuse.
Fish Facts for Kids
Got fish questions? We’ve got fish answers!
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Fish take in water through their mouths, and pass it through a special chamber to run over their gills, which are on the outside of their body.
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Most fish don’t sleep in the same way humans do, but they do rest. They enter extended periods of reduced movement and metabolism.
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Most fish can’t close their eyes because they don’t have eyelids.
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It’s unclear if fish experience the feeling of thirst the same way humans do, but fish do need water to survive.
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It actually depends on the fish! Freshwater fish do not need to drink water, because water just passes into their bodies from the water around them, mainly through their gills. Saltwater fish, on the other hand, need to actively drink water, because they’re actually constantly losing water to the water around them.
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Yes; studies have shown that fishes feel and respond to pain.
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Not really. Drowning usually means not being able to breathe because you’re surrounded by liquid. Fish don’t have that problem, since they actually need to be surrounded by liquid. A fish could suffocate due to lack of oxygen, though, if the liquid around it didn’t have enough oxygen in it.
More Answers to Marine Biology Questions from Kids
Why are sharks such good hunters? How do octopuses change color so fast? The Tappity Marine Biology Library has interactive lessons with answers to those questions and more!
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