Hello Nghi,

Cats, humans, and fish all breath for the same reason. We need oxygen. Oxygen is one of the things our bodies use to make energy.

Just like the hungry feeling you get when you haven’t eaten, your body uses oxygen to keep everything running. Unlike the breaks you take between meals, the breaks you take between breathes are much shorter. Most people take about 12 breaths per minute.

While it may seem like we breath only oxygen, there are lots of other gasses in the air. When we breath in, our lungs fill up with all this gas. The lungs take the oxygen out of the air and breath out all the rest of the air our body doesn’t use.

In addition, we breath out carbon dioxide. It’s a gas our body produces when it makes energy. Just like how your body sweats when you play sports, your body makes carbon dioxide when it breathes.

Fish also use oxygen to keep their bodies running, but the oxygen that they use is already in the water.

Their bodies are built differently than ours. Humans and cats have lungs, while fish have gills.

That’s what I found out when I went to visit my friend Michael Berger. He’s a biologist at Washington State University.

You can see a fish’s gills when you look at their faces. They are lines on the sides of a fish’s face. The gills are also inside the fishes’ body, but those can’t be seen from the outside– just like our own lungs.

Berger explained that you can see a fish breathe in water because their face gets bigger when it’s full of water. Just like when you take a big bite of food.

First, the water goes into the fishes’ mouth and through the gills. As the water leaves the gills it returns to the ocean. Additionally, the carbon dioxide the fish creates is also removed as the water leaves the gills.

Berger shared a fun fact with me during our visit: Fish and other animals with gills are able to get oxygen to breathe because their blood flows through the gills in the opposite direction of water. If their blood flowed through the gills in the same direction as the water, the fish would not be able to get as much oxygen from it.

The gills are a like a filter and they collect all the oxygen the fish need to breath. After the gills pick up the oxygen, it is sent throughout their blood and fuels their bodies.

That’s why it’s important to leave fish in their home. Without water, they are unable to get the oxygen needed to stay happy and heathy.

If humans would like to breath underwater like fish, they can use a snorkel to experience life like a fish. Most snorkels kits include a mask and a mouth piece. The mouth piece is attached to a tube that reaches above water. That way, humans can keep breathing air while their mouth and nose are under water.

Amanda Tomchick (and Dr. Universe)


Amanda Tomchick contributed this article. She is a student in the Edward R. Murrow College of Communication at Washington State University.