Water in oceans and seas contains a significant amount of dissolved oxygen. Yet, if a human tried to breathe underwater, survival would be impossible. Meanwhile, marine creatures do this naturally and effortlessly. This raises a fascinating question: how do fish extract oxygen from water? And do all marine animals breathe in the same way? In this article, we’ll explore how different marine life forms respire and the key differences between fish and marine mammals, such as whales and dolphins.
Respiration as a vital process
Oxygen keeps life alive. It fuels every cell, giving living things the power to move, grow, and stay alive. Humans get oxygen through their lungs, pulling it from the air with each breath. The lungs send it into the blood, which carries it to every part of the body. In return, carbon dioxide leaves as waste. But for creatures under the sea, things work differently. There’s no air to breathe, only water. Over millions of years, marine life developed amazing ways to take in the oxygen hidden within it.
How do fish breathe underwater?
Fish don’t have lungs like we do. Instead, they breathe through special organs called gills. These gills handle the vital job of swapping gases — taking in oxygen and letting out carbon dioxide. Each gill is made of thin, delicate filaments filled with tiny blood vessels. That’s what gives them their bright red color. Most fish have four pairs of gills, but some, like sharks, can have as many as seven. When a fish opens its mouth, water flows in and washes over the gills. The blood inside the filaments collects the oxygen dissolved in the water and releases carbon dioxide in return. Then, the used water slips out through the gill openings — just like water draining through a strainer.
The challenges of breathing underwater
Although fish appear well adapted, underwater respiration is actually a demanding process. Water contains only about 8 milligrams of oxygen per liter, while air contains nearly 210 milligrams per liter — over 25 times more. Furthermore, oxygen levels drop significantly in deeper waters, meaning fish must rely on highly efficient oxygen-extraction systems to survive in such conditions.
Dual breathing in certain species
Not all fish depend solely on gills. More than 450 fish species can breathe air directly using dual respiratory systems, which combine gills, lungs, or even skin surfaces.
Examples include:
- The Mudskipper: Native to Southeast Asia, it can live up to six consecutive days outside the water, breathing directly through the air.
- The Catfish: Known in Egypt as Qarmout, this fish can survive on land as long as its skin remains moist.
Marine mammals — a unique case
Whales and dolphins are not fish, but marine mammals that breathe air through lungs. They have a special opening on top of the head called a blowhole, which closes tightly while diving and opens when they reach the surface to inhale air. Whales can store large amounts of oxygen in their bodies, allowing them to stay submerged for up to 60 minutes, while dolphins can usually hold their breath for 8–10 minutes.
Now you understand how marine life breathe underwater
Respiration in marine life is one of the most remarkable examples of biological adaptation. While fish use gills to extract oxygen from water, marine mammals rely on lungs to breathe air, illustrating the extraordinary diversity and intelligence of life beneath the waves. Understanding these mechanisms deepens our appreciation of marine biology and contributes to global conservation efforts aimed at protecting the delicate balance of ocean ecosystems. If you’re inspired to explore this hidden world yourself, Hurghada Today offers unforgettable sea trips where you can witness the beauty of marine life up close.
