Just like humans, fish need oxygen to survive, so how can fish breathe underwater? Scientists have conducted a study that shows the method by which these animals can breathe underwater is a relatively simple one.
The method by which fish breathe underwater
Oxygen helps release energy from the sugar chemical glucose in a process called respiration. Respiration also releases carbon dioxide, a process found in both humans and fish when breathing.
Humans inhale oxygen from the air through the mouth and nose, reaching the lungs and thus breathing takes place. In the case of fish, this process is more different. In order to breathe, fish must remove oxygen molecules dissolved in the water, according to the Iowa Department of Natural Resources.
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The amount of oxygen in air is much higher than the amount of oxygen in water, however. This means that fish have a much more difficult breathing process than humans. Fish take in water in their mouths, just as we take in air by opening and closing our lips.
This water is then filtered through gills, organs that have lots of filaments made up of protein molecules. The filaments look like little brushes. They have thousands of tiny blood vessels to help oxygen get into the blood, even more blood vessels than in human lungs.
The larger number of blood vessels in fish provides a much larger surface area, which helps them pull dissolved oxygen from the water and release carbon dioxide back into the water. The difference in “design” between lungs and gills is the main reason why humans cannot breathe underwater.
With the help of gills, fish can filter oxygen from the water
Labyrinth fish
About 75 percent of the oxygen that passes through fish gills is extracted, according to the American Museum of Natural History. Fish also use less energy to live than mammals like humans, so they need less oxygen.
However, they still need oxygen. This means that low oxygen water is just as deadly to fish as low oxygen in the air can be to us. Anoxic and hypoxic zones, sometimes called dead zones, are places in the ocean where there is so little oxygen that fish cannot survive.
Gills need water to maintain their structure and prevent damage to the thin tissues. Like people drowning under water, fish can drown in air. If their gills are exposed to the open air for too long, they can deteriorate, causing the fish to suffocate. They are especially suited to underwater life, just as lungs are to life on land!
Labyrinthfish are named for their lung-like “labyrinth” organs, which have numerous labyrinth-like compartments. Those organs help certain species of fish, including Betta, Gourami, and Paradis fish, to breathe air, just like humans. They also have gills so they can breathe dissolved oxygen in the water as well.
For millions of years, these fish and their ancestors lived in waters with very low oxygen levels. Evolution has favored any fish that are born with advantages that help them make the most of whatever oxygen they can find. Labyrinth fish can survive even out of water.