How do Fish Breathe?

By: Spencer Reichart

The water that fish "breathe"!

Fish are unique creatures that can live where we can't go; the water. It is a lot harder for fish to breathe underwater but luckily their lungs are smaller so their demand for oxygen is lower. The air that we breathe is approximately 21% oxygen or about 210,000 parts per million. But water on the other hand is about 3-4 parts per million of dissolved oxygen that fish's gills can extract. The oxygen that fish breathe is not the oxygen in H2O. Instead, the fish are breathing O2 (oxygen gas) that is dissolved in the water. For a comparison, if the water is at 15 degrees celsius then there is 30 times more oxygen in the air than in the water.Fish are amazing little creatures so let's learn more about them!

The Functions of Gills!

Gills are an organ that are specific to only fish. Fish's gills are feathery, which gives them a large surface. They can be very good at extracting oxygen from the water, allowing some fish to be very fast swimmers. The main reason why gills only work for fish is because they are cold-blooded creatures which reduces their demand for oxygen. Did you know that gills have a car radiator-like appearance? Functionally, the mechanism for pumping water over the radiator-like gills seems to vary depending on the species of fish. Most fish have four gills on each side, consisting of a main bar-like structure that has numerous branches coming off of it. As the fish raises the floor of their mouth, an inward fold of skin forms a valve of sorts which doesn't allow water to rush out. But the question we all want to know is why we can't swim underwater. So let's answer it!

Why are fish so unique?

Most of us would love to go swim with all the underwater wildlife without all of the dangers of drowning. Unfortunately at this moment in time it is not possible. There are many reasons why. Humans cannot breathe underwater because our lungs do not have enough surface area to absorb enough oxygen from water, and the lining in our lungs is adapted to handle air rather than water. Warm-blooded animals like whales breathe air like people do because it would be hard to extract enough oxygen for their large lungs using gills. Another reason we cannot breathe liquid water is because the oxygen used to make the water is bound to two hydrogen atoms, and we cannot breathe the resulting liquid. The oxygen is useless to our lungs in this form. There has been experiments with humans breathing other liquids, like fluorocarbons. Fluorocarbons can dissolve enough oxygen and our lungs can draw the oxygen out. So even though we can live right alongside fish at the moment maybe in the future scientists will invent something to let us explore other wonders of the ocean.