When we think of fish, we usually think of salt water creatures that live in the ocean. But there are freshwater fish too, and they all breathe air. Why? Fish breathe air because they evolved to do so. Freshwater fish evolved from fish that lived in lakes and streams, which are full of oxygen. When they moved into the ocean, they had to find a way to survive in an environment with less oxygen. So they developed lungs and were able to breathe air.
Fish breathe air
Fish breathe air because they have a caudal fin and gills on the bottom of their bodies. Caudal fins help fish swim by moving their tails side to side. Gills are small, tissue-rich organs located on the lower sides of a fish’s body that extract oxygen from water.
How fish breathe air
Fish breathe air through their gills. Gills are special organs found on the top of the head and down the sides of the body that help fish extract oxygen from water. When a fish expels water, it also expels gas bubbles that contain oxygen. The gas bubbles travel up the fish’s nasal passage and into its mouth, where they are dissolved in saliva and swallowed.
What regulates fish breathing air
Fish breathe air by taking in oxygen and exhaling water. The gills of fish are located behind their heads and in front of the body. They use these to extract oxygen from the water and then expel it through the mouth or nose.
Many fish can breathe air, but some cannot. Fish that can breathe air include catfish, goldfish, and most tetras. These fish get their oxygen from the water they live in or surface waters. Many fish that cannot breathe air lack a lung sack and instead extract oxygen through their gills. These are typically bottom-feeders like mudskippers or minnows.