In 2019, a runner named Eliud Kipchoge made history by finishing the Vienna Marathon in just under two hours. This was a big deal because many people thought it was impossible to run a marathon that fast. Scientists found that elite runners like Eliud can take in a lot more oxygen than regular people, which helped him achieve this amazing feat.
Even though Eliud is an incredible runner, he still can’t beat fish when it comes to breathing efficiently. Fish are some of the best breathers on the planet, which is super important because they live in water where oxygen levels are much lower than in the air.
Fish use special organs called gills to breathe. They usually have four pairs of gills, all tucked inside gill chambers. These chambers are protected by gill covers, also known as opercula, which help fish breathe underwater.
Here’s how it works: Fish close their gill covers and take in water. Then, they open the covers, which creates a pressure change that pulls water through the gills. The gills have tiny filaments with lots of small blood vessels called capillaries. These capillaries are covered in even smaller extensions called gill lamellae, which increase the surface area for breathing.
As water flows over the capillaries, oxygen from the water is absorbed into the fish’s blood, and carbon dioxide is released back into the water. This process is super efficient underwater but doesn’t work well on land because there’s not enough pressure difference.
Inside the gills, blood flows in the opposite direction to the water. This setup, known as a counter-current system, makes gas exchange very efficient. Fish gills can absorb about 75% of the oxygen that passes through them, which is twice as much as human lungs can extract from air.
Fish breathe more often than humans do. While humans typically breathe 12 to 18 times a minute, fish can move water over their gills 20 to 80 times a minute. This allows them to take in a lot more oxygen.
In deep waters where oxygen is scarce, fish have to work harder to breathe. They increase their gill ventilation and have hearts that pump lots of oxygen-rich blood. Some fish, like the Australian lungfish, have both gills and lungs. This lets them breathe air when water levels are low.
Luckily, most fish don’t need such extreme adaptations because 71% of the Earth’s surface is covered in water, giving them plenty of space to live and breathe comfortably.
Using materials like paper, cardboard, and straws, create a model of a fish’s gill system. Focus on demonstrating how water flows over the gills and how the counter-current system works. Present your model to the class and explain the breathing process of fish.
Research and create a Venn diagram comparing fish and human breathing systems. Highlight the differences in efficiency, structure, and adaptation to their environments. Share your findings with a partner and discuss why these differences exist.
Conduct a simple experiment to measure oxygen levels in water. Use a dissolved oxygen test kit to test different water samples (e.g., tap water, pond water, aquarium water). Discuss how these levels might affect fish breathing and survival.
Participate in a role-playing game where you simulate being a fish in different environments. Consider factors like oxygen levels, water temperature, and pollution. Discuss strategies fish might use to survive and how their breathing adaptations help them.
Prepare questions and conduct a virtual or in-person interview with a marine biologist. Focus on how fish breathing adaptations help them survive in various aquatic environments. Share the insights you gain with the class through a short presentation.
In 2019, Eliud Kipchoge completed the Vienna Marathon in one hour, 59 minutes, and 40 seconds. This remarkable achievement broke the two-hour barrier that many runners had previously considered impossible. However, some researchers were not as surprised. Recent studies have shown that elite runners can take in twice as much oxygen as non-runners, which likely contributed to Eliud’s success.
When it comes to breathing efficiently, even the best runners cannot compete with fish, which are among the most efficient breathers on Earth. This is particularly relevant given the low oxygen levels in their aquatic environments. Fish primarily breathe through gills, which are branching organs typically found in four pairs, all enclosed in gill chambers. These chambers are protected by opercula, or gill covers, which are essential for underwater breathing.
When fish breathe, they first close their gill covers and take in water. They then open the opercula, creating a pressure differential that pulls water through the gills. The gills consist of thread-like filaments spaced along a gill arch, covered in numerous small blood vessels called capillaries, as well as tiny extensions known as gill lamellae that increase the gill’s surface area. As water flows over these capillaries, dissolved oxygen is absorbed into the fish’s bloodstream, while carbon dioxide is released back into the water.
This breathing technique is effective underwater, but it does not work on the surface due to insufficient pressure differential. However, it is highly efficient below the surface. Inside the lamellae, blood flows in the opposite direction to the water, optimizing gas exchange through a counter-current system. Gills can absorb approximately 75% of the oxygen passing through them, which is double the percentage that human lungs extract from a breath of air.
Fish also breathe more frequently than humans. While the average adult human breathes 12 to 18 times a minute, most fish pull water over their gills 20 to 80 times a minute, allowing them to process significantly more oxygen.
In deeper waters, where oxygen levels can be very low, fish rely on increased gill ventilation and hearts that pump high volumes of oxygenated blood. Some species, like the Australian lungfish, have adapted to survive in environments where water levels drop significantly. These fish possess both gills and lungs, enabling them to take air from above the surface when necessary.
Fortunately, for most fish, such extreme adaptations are not required, as 71% of the Earth is covered in water, providing ample opportunity for these aquatic animals to thrive.
Fish – A cold-blooded animal that lives in water, has fins, and breathes through gills. – Many fish swim in the ocean, using their fins to move and their gills to breathe.
Breathing – The process of taking air into and expelling it from the lungs. – Breathing is essential for humans to get the oxygen they need to survive.
Gills – Organs that allow fish and some other aquatic animals to breathe underwater by extracting oxygen from water. – Fish use their gills to extract oxygen from the water as it flows over them.
Oxygen – A gas that is essential for most living organisms to breathe and produce energy. – Plants produce oxygen during photosynthesis, which is then used by animals for breathing.
Water – A liquid that is essential for life and makes up a large part of the bodies of most living organisms. – Fish live in water and rely on it for their survival and to breathe through their gills.
Blood – A fluid in the bodies of animals that delivers necessary substances such as nutrients and oxygen to cells. – The heart pumps blood throughout the body, carrying oxygen to the cells.
Carbon – A chemical element that is a fundamental component of all living organisms and is found in carbon dioxide. – Plants absorb carbon dioxide from the air during photosynthesis.
Exchange – The process of swapping one thing for another, such as gases in the lungs or gills. – In the lungs, there is an exchange of oxygen and carbon dioxide between the air and the blood.
Lungs – Organs in the body that allow animals to breathe air and exchange gases with the blood. – Humans use their lungs to take in oxygen and expel carbon dioxide.
Pressure – The force exerted by a substance, such as air or water, on a surface. – The pressure of the water increases as you dive deeper into the ocean.
