How do Fish Breathe Underwater ? Fishinaquarium

How do Fish Breathe Underwater


When it comes to breathing underwater, even a simple thought of it can give us an uncomfortable feeling. But then have you ever thought, how do fish breathe underwater so effortlessly? Well, they are created in a way that helps them to stay and breathe easily underwater.

So, how do fish breathe underwater? Well, they breathe through their sole respiratory organ, gills. As water passes through their gill’s surface, the tissues present in it absorb dissolved oxygen from the water and deliver it to their body to fulfill their breathing requirements.


How do fish breathe underwater?


Fishes are born with gills. Their respiratory organ is created to be highly efficient in extracting dissolved oxygen from the water. So, fishes breathe through their gills underwater, which renders a constant supply of fresh oxygen to them.

Gills are positioned right under the operculum of fish. It is known as the gill slit. Most fishes come with four pairs of gills, while others have even up to seven pairs of gills.

So, how do fish breathe underwater so flawlessly? The process of breathing starts as fishes intake water from the ocean through their gill’s surface. The water passes through the feathery filaments located on their gills.

Usually, their gills remain filled with blood. And when water flows through, their gill filaments absorb oxygen from the water and then move the oxygen to their bloodstream. After that, the fish’s heart pumps oxygenated blood throughout their body to meet their bodily requirements.

Similarly, carbon dioxide in their blood passes out of the fish’s body through their gill’s surface into the water.


Why can’t fish breathe out of water?


Similar to us, even fishes require oxygen to breathe while they swim underwater. Then, why can’t fish breathe out of water? The air we breathe also contains oxygen. Then, why is it difficult for them to breathe oxygen from air?

Well, fishes actually don’t breathe oxygen from H2O. Instead, their gills extract O2, which remains dissolved in water. This process of drawing out dissolved oxygen is quite complex.

Water is highly dense than air, and also air has 20 times more oxygen than that present in a similar volume of water. Hence, fishes need to put more effort into extracting oxygen from water while moving it. However, being cold-blooded creatures, they do not require too much oxygen to survive. So, their minimal breathing requirement is easily fulfilled through gills.

Why can fish breathe underwater and humans can’t?


As we breathe in the air, the oxygen present in the atmosphere travels through our nose, down to the trachea to reach the lungs. Now, our lungs get branched into smaller airways, which aids breathing. Oxygen tends to pass through the membranes of the lungs into the bloodstream. Waste gases like CO2 initially diffuse out of the blood, which subsequently gets expelled as we breathe out.

Now, when it comes to fishes, even these species need oxygen for better living. However, their lungs are not designed for extracting oxygen from the air. Instead, as water passes through their gills, the organ draws out oxygen from the water and eliminates wastes out of their body.

But unfortunately, we humans are not born with gills. We cannot extract oxygen out of the water as fishes do. Thus, we tend to die or feel an urgent need to breathe while submerging deep into the water.

Though most mammals are incapable of breathing in water like us, aquatic creatures can breathe easily while living under the water.

Nevertheless, many marine mammals like dolphins and whales live in the water, but they do not extract fresh oxygen from dissolved oxygen in the water. Instead, they possess lungs like us, which they use to breathe in oxygen and exhale carbon dioxide directly to and from the air by often coming up to the water surface.

Well, another reason we cannot breathe under the water is that due to the water molecules that don’t contain a sufficient amount of oxygen as present in the air. The water molecules are made up of covalently bonded gases. It contains two hydrogen atoms and one oxygen atom. And it needs a lot of energy to break the atoms apart and release the oxygen molecules.

But the lining in the human lungs is not adequately designed to carry out such a process. A person would probably die before having appropriate oxygen rates to resume the breathing process. Also, human lungs do get benefitted from inhaling oxygen, which is in its atomic state.

On the contrary, fishes can easily breathe in dissolved oxygen through their specialized organ, gills, which helps them have easy respiration.

What do fish use to breathe underwater?


While learning how can fish breathe underwater, it is essential to know what do fish use to breathe underwater. Well, fishes typically use their gills for breathing properly underwater. While humans cannot breathe under the water without any aid, fishes are blessed with gills.

We typically cannot breathe underwater, as our lungs do not have sufficient surface area for absorbing enough oxygen from the water. At the same time, the lining in our lungs is capable of handling air rather than water.

But fishes possess gills, which they use to breathe underwater, as their gills are made to fulfill this purpose itself. Fishes are usually cold-blooded species; hence, they have a reduced oxygen demand, unlike warm-blooded mammals. So, their minute oxygen requirement can be easily met with the proper functioning of their gills.

How can a fish breathe underwater?


The respiratory system of fish is completely different from ours. Though fishes breathe in oxygen like us, their process of breathing is too diverse. They require oxygen to offer sustenance to their cells.

Fishes come with specific specialized structures that help them to execute their respiratory functions. These structures aid them in inhaling oxygen that remains dissolved in water.

So, are you wondering what these special structures are? Well, it’s the gills. Fishes have gills on either side of their head, containing various feathery elements known as gill filaments. These filaments offer a broad surface area for better exchange of gases underwater. The large surface area of their gills is crucial for the successful exchange of O2dissolved in water.

The filaments present in the gills of fishes are nicely organized in rows inside the gill arch area. Each of the filaments of the fish’s gill contains lamellae. These structures appear like discs that are supplied with blood capillaries.

As blood moves in and out through the small blood vessels, the absorbed oxygen gets processed. Although the gills of fish occupy a tiny section of their body, the extensive respiratory surface formed by their gill filaments facilitates highly efficient gas exchange to render effective breathing.

As soon as fishes absorb oxygen-rich water through their gills, the water moves over the filaments of their gills, and the blood within the capillary network absorbs the dissolved oxygen. Then the circulatory system of the fish delivers oxygen to all tissues of the body.

Simultaneously, fishes eliminate carbon dioxide in the same way through their gills. It gets released from their body as water moves out through the gills via the openings situated on either side of their throat or through the operculum.

Some fishes like sharks, lampreys, etc., have multiple gill openings for enhanced breathing. On the other hand, bony fish like rohu have only a single gill opening on their side. Basically, the number of gill openings present in the fish depends on their oxygen and respiratory requirements.

How do fish get oxygen for respiration?


So, are you wondering, how do fish get oxygen for respiration? Well, to produce a sufficient amount of oxygen for breathing, fishes need to pass a large volume of water through their gills’ surface.

As they swim forward, water comes in contact with their gills and gets absorbed through the surface. Within their gills, the water is processed to produce a sufficient amount of oxygen, which is necessary to meet their breathing needs.

Their body parts work like a pump, which keeps the water moving over the gas absorption surface of their gills. Hence, in this way, they get charged with a proper amount of oxygen from time to time.

Why do fish breathe underwater?


Now that you know how fishes breathe, don’t your inquisitive mind come up with another related query, why do fish breathe underwater? We’re sure it must have.

Well, fishes are not created in that way, which can help them breathe oxygen directly from the air. Their gills need to be wet with a continuous flow of water to perform a steady respiratory cycle.

As a fish comes onto the land, its gill will still work till the time it is wet. As air blows through the gill surface, it starts to become dry, preventing it from producing oxygen anymore. It ultimately leads to the fish’s death. Thus, fishes need to breathe underwater with a consistent flow of well-oxygenated water to stay alive.

Why do fish spend a lot of energy removing oxygen from water?


Fishes usually extract dissolved oxygen from the water through their respiratory system to fulfill their breathing cycle. But extracting dissolved oxygen from the water molecules is not easy.

Since atmospheric air contains more oxygen than water of the same volume, it becomes tougher to extract the oxygen out of the latter one. Thus, fishes need to put more effort and energy into extracting dissolved oxygen from water. It looks like marine life is tougher! What do you say?



So, we hope, by now, you’ve got your answer to the question, how do fish breathe underwater. Well, it feels pretty strange to know that while those marine cuties hover here and there so effortlessly, it takes a lot of their energy to extract oxygen just to breathe properly.

So, if you are keeping fishes in your tank, make sure it has adequately oxygenated water so that your tiny aqua pets can breathe effortlessly. Continuous ease of breathing helps fishes to stay healthy and charged with immunity. Also, continuous breathing helps them to prevent getting suffocated.