How do fish breathe underwater?


Fish are aquatic vertebrate animals, normally covered with scales and finned. Each species has its peculiarities but, as with terrestrial animals, they all use a breathing system that allows their life underwater. Do youHow fish breathe?

Fish breathe thanks to gills, some extensions of the skin, structures with hair filaments, located on both sides of the pharynx and that allow the exchange of gases. Unlike lungs or tracheas, these are external organs, holes that laterally communicate the digestive tract with the outside.

In essence, what fish do is to use the membranes or operculi gills to take advantage of the oxygen that they take from Water through the mouth and spread it through all the cells they have in the body. In the same way they expel the environment carbon dioxide surplus. The process takes place cyclically and is as effective as we do outside the aquatic environment.

Although less, it is true that there are also fish with lungs, forced to surface and take the air outside to take it to the gills.

Other times, outside breathing is part of the adaptation of some fish that are forced to survive in shallow waters and with hardly any oxygen.

The gills of the fish

The gills of the teleost fish, which are the majority of fish with the exception of sharks, rays, lampreys and mixines, are found at both sides of the head. From outside we can see the opercular cavity, which is the part of the "fish face" that opens outward and is called an operculum. Within each opercular cavity, we find the gills.

The gills are structurally supported by the gill arches, which are four. From each gill arch, two groups of filaments called gill filaments come out that are arranged in a "V" shape with respect to the arch. Each filament overlaps with neighboring filaments, forming a fabric. In turn, these gill filaments they have their own projections called secondary lamellae. Here the gas exchange takes place, the fish take oxygen and release carbon dioxide.

The fish drinks water through the mouth and, through a complex process, releases the water through the operculums, previously passing through the lamellae, where oxygen is captured.

Fish respiratory system

The fish's respiratory system is called buco-opercular pump. The first pump, the buccal, exerts positive pressure, so it sends the water to the opercular cavity and, in turn, this cavity by negative pressure, sucks the water from the oral cavity. In summary, the oral cavity pushes the water into the opercular cavity and it sucks it.

During a breath, the fish open the mouth and the area where the tongue is low, causing more water to enter, because the pressure decreases and the water enters the mouth into the mouth in favor of a gradient. After shut your mouth and the oral floor rises increasing the pressure and causing the water to pass into the opercular cavity, where the pressure is lower.

Then, the opercular cavity contracts, forcing the water to pass through the gills where the gas exchange and leaving passively through the operculum. When the fish opens its mouth again, a certain return of water may occur.

Like us, fish need oxygen to live

Aquatic animals have very different characteristics from the rest. While mammals, birds and reptiles need air to continue living, fish they are able to remain underwater without going out to the surface. In fact, this would cause his death. At this point it is inevitable to ask ourselves the following question: How do fish breathe into water?

Fish live on diluted oxygen

Although they live in this environment, they also need oxygen to stay alive. To do this, they have a very particular respiratory system, which manages to extract dissolved air from water. They do it thanks to the gills, membranes located on the sides of their body. When the animal opens and closes the mouth, the liquid enters inside through them and that is when the blood vessels absorb the necessary oxygen.

Do fish have lungs?

Although it may seem contradictory, the evolution has caused the appearance of dipnoos or lungfish. Within phylogeny, they are classified in the Sarcopterygii class, for having lobed fins. It is believed that these fish with lungs are closely related to those first fish that gave rise to land animals. There are only six known species of lungfish and only about some of them we have knowledge about their conservation status. Some do not even have a common name.

The species of fish with lungs are:

  • American mud fish (Lepidosiren paradoxa)
  • African lungfish (Protopterus annectens)
  • Marble lungfish (Protopterus aethiopicus)
  • Protopterus amphibius
  • Protopterus dolloi
  • Queensland or Australian lungfish (Neoceratodus forsteri)

Despite being able to breathe air, these fish are closely linked to water, even when it is scarce due to droughts, they hide in the mud protecting their body with a layer of mucus that they can make. His skin is very desiccation sensitive, so without this strategy they would die.

If you want to read more articles similar to How do fish breathe?, we recommend that you enter our Curiosities section of the animal world.

Do you know what the operculum is?

Another element of great consideration in the respiratory system of fish is the operculum. This allows the absorbed water to remain inside the body. When the mouth is closed, the operculum is discovered to let the fluid pass through the gills. And the rest is history.

Temperature directly affects the amount of oxygen in the water.

Given the complexity of this way of life, the environment in which the fish live is very important. Especially when we talk about pets or company. We must be aware of many factors for the fish to survive. Temperature, for example, is essential, because directly affects the amount of oxygen present in the water. The hotter, the less quantity. For this reason, it is essential to know the requirements and provide your friend with a suitable place to live.

Of course, you should keep in mind that each copy is different. While tuna has a more sophisticated respiratory system, bony fish need that water and blood circulate in opposite directions. As you can see, we are facing a kind of the most unique. And the ocean has great surprises.

What are gills

Gills they are membranes where fish take oxygen. They are located in the lateral parts, between the pharynx and the animal's mouth. Water is introduced through them when the fish closes and opens its mouth. It is at that time when the blood vessels of the fish absorb the necessary oxygen and transports it through the bloodstream.

Fish respiratory system

The vast majority of fish have an area that covers them called opercle. Each time the fish opens its mouth, the operculum closes, causing the water to remain inside. Instead, when the mouth is closed, the operculum opens and allows the passage of water through the gills.

Water passes from mouth to gill chambers located on both sides of the head. The gills contain some laminar filaments called lick them. The water flowing through the gills, allows the oxygen it contains to be transmitted to the blood thanks to the blood vessels of the lamellae and the filaments.

In the same way, the carbon dioxide in the fish's blood It disperses in the water and is expelled from its body. For that reason they can stay submerged underwater all the time. Its anatomy is perfectly adapted to the liquid element.

How do fish breathe underwater

There are some fish, such as tuna, which do not have such a sophisticated respiratory system, and need to have their mouths open for longer to get enough oxygen to absorb from the water.

But attention, animals like dolphins or whales do not breathe like fish. You can get more information by clicking on their names. 😉

Now you know how fish breathe. But does it work the same in every part of the world? We will see it in the following section:

Types of breathing in fish

The amount of oxygen present in the water varies depending on its temperature. Thus, in cold waters the amount is greater than in warm waters. This is one of the reasons why fish need different habitats.

Those who need less oxygen to live in warmer waters. On the other hand, those that require more quantity live in colder waters.

In bony fishes, the exchange system between oxygen and carbon dioxide works much better if it is carried out against the current. This means that for optimal operation, water and blood have to circulate in opposite directions. Similarly, this system serves to remove impurities from the blood.

And remember, unlike many other animals, fish need to be in the water to live. The gills only work inside this liquid, outside it they cannot perform their vital function. For that reason, if you decide to have them as a pet, keep in mind that the fish's respiratory system is different from yours and you should provide them with an appropriate environment.

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