Fish, like mammals and other animals that populate the earth, need oxygen to survive and carry out all their activities. To swim, reproduce, eat, etc., they need large inputs of energy and oxygen that they cannot get through the air.
Just as we cannot breathe in the water without drowning, fish, if they are out of the water long enough, also die. So, how do fish breathe? Where do they get the oxygen?, in UnComo.com we are going to solve it, explaining how fish and other aquatic animals have developed a complex system that allows them to obtain the oxygen contributions necessary to live, even if they are underwater.
How fish breathe
Fish breathe through complex organs called gills, which in most species are located on both sides of the head, under a mobile membrane that protects them and is called the operculum.
Since oxygen dissolves 30 to 40 times worse in water than in air, fish and other aquatic animals have been forced to evolve so that they can live in water and get the oxygen they need.
In most fish this system is the gills, which through the so-called countercurrent exchange, manage to transfer oxygen from the water to their blood, for this they swallow water through the mouth, forcing it to leave through the gills and there, they have a dense network of blood vessels and blood flow that circulates in the opposite direction to the water. In this way it can be ensured that it will optimize this exchange to the maximum, in fact, the fish are left with up to 85% of the oxygen contained in the water they filter.
The gills of fish
How do they get oxygen out of the water? Although we have already explained a little the functioning of the gills, perhaps it is a bit complicated to understand the whole process.
In modern bony fish, scientifically called teleosts and which are the majority today, the mouth and its cavity communicates with openings on the side of the pharynx, which are called gill slits, from which the gills develop. These are protected by the opercula, the solid structures located on each side of the head, the typical slits on the sides so characteristic of fish.
Between the gill slits pass curved structures called gill arches, they are two rows of filaments that come together forming a V. From these filaments are born some folds or secondary sheets, between 10 and 40 each mm, formed by tissue and a large number of blood vessels.
In this way, when the fish opens its mouth, the water full of oxygen enters through it, it passes through this entire structure and exits through the operculum, but in between, it circulates in the opposite direction through the sheets, which trap all the oxygen they can.
Other methods of respiration in fish
By lungs
There are at least 400 species of teleosts that use air to breathe, the vast majority freshwater fish, although almost all also retain gills and use each system at will.
Lung breathing is used when the oxygen level of the water falls, such as when the temperature rises, since the higher the temperature, the greater the need for oxygen.
However, there are also fish that only breathe through lungs, an example of this is the Lepidosiren, a South American species that has lungs with two lobes and very simple gills, so they need to breathe air if they do not want to die.
By the skin
Most fish, when they are born and have not yet developed respiratory organs, take oxygen through the skin, although as the animal grows and develops the gills breathing through the skin becomes more residual. However, in some adult fish, respiration through the skin can account for up to 20% of the total oxygen supply.
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