How do marine animals drink fresh water?

Everyone must have heard this saying: "Even if you are dying of thirst at sea, you can't drink sea water." Since sea water cannot be drunk, how do marine animals drink fresh water?

Why can’t we drink sea water directly?

Some people say that sea water is very salty and the more you drink it, the thirstier you become.

Of course, saltiness is one reason, but do you know why it is so salty?

This has to start with the origin and development of the ocean. In the beginning, the ocean gathered various water sources on land, and with the changes in the geological environment, the ocean gradually formed.

When rivers carry seawater resources, they also carry various substances, mainly salts.

Since seawater cannot exchange with other water bodies, these substances accumulate in the seawater. During this period, the water in the seawater continues to evaporate and participate in the water cycle. Even if there is continuous dilution with fresh water, it still cannot keep up with the speed of seawater salinization, and the salinity of the seawater becomes higher and higher.

In fact, we can simply think of the sea as a huge "static lake" with only water flowing in but not out. It is easy to understand why the water in it is so salty.

Nowadays, the content of various substances in seawater seriously exceeds the standards acceptable to organisms, so seawater is not suitable for direct drinking.

In addition, the human body itself contains a certain amount of salt, and the salt content of seawater is more than three times that of the human body. When the human body takes in seawater, the salt in the seawater will force the body to absorb salt, causing the concentration to rise rapidly.

The result is that the fresh water in the cells is lost, and drinking sea water when hungry and thirsty is tantamount to suicide. The same is true for marine organisms.

In order to survive, creatures in the ocean have evolved unique purification organs.

Miraculous purification organ

Fish, the most numerous and diverse species in the ocean, use chloride-secreting cells in their gills to filter seawater.

The chloride-secreting cells in the fish's gills are like a miniature processing plant. On the one hand, they extract the salt from the water, and on the other hand, they retain qualified water sources.

As we all know, fish gills are their respiratory organs. When obtaining oxygen from the water, they will inevitably ingest a small amount of seawater.

Over time, the salt from the seawater will accumulate in the fish's body, which will make it salty. How do fish deal with this situation?

The internal structure of some fish is of the "rectal" type, and unpurified water can be discharged directly through the anus.

Other fish will carry out secondary purification within their own bodies, using their own cells, liver and other parts to regulate and reduce the residual salt in the body.

The internal organs can purify a small amount of seawater and mainly play an auxiliary role.

However, there is one creature in the ocean that dares to confront the sea water, and that is the whale.

Whales are not fish, but marine mammals, which are closer to terrestrial creatures. When obtaining fresh water, they directly swallow large amounts of sea water and then purify the water through their powerful kidneys.

Of course, it is impossible for whales to purify all the seawater, and some of the seawater that cannot be purified will be discharged along with the whales' activities.

At this point, everyone may have a question: whales drink the sea water in one gulp, so aren’t they afraid of the reverse effect of the sea water on their cells?

Of course whales are not afraid, because there is a very thick layer of special mucous membrane in their intestines and stomach. On the one hand, it is to prevent the whale from eating sharp objects and scratching its intestines when it "swallows" in one bite.

For example, sperm whales like to forage for giant squid in the deep sea. The squid's skull is very hard and sharp, and not easy to digest. Only if the stomach and intestines are strong enough can they avoid being scratched by the squid's skull.

It is worth mentioning that after the giant squid's skull was excreted by the sperm whale, it fermented for decades to form "ambergris", which is more valuable than gold.

On the other hand, the special mucous membrane in the stomach can also effectively prevent harmful substances from being absorbed by whales.

Before whales absorb food and water, they need to go through three levels of digestion. Each level must undergo strict screening, and those that fail the test will be excreted as waste.

Therefore, even a whale of such a huge size can live leisurely in the ocean.

Fresh water from crying

The next creature has an even more powerful ability to purify seawater. It is a sea turtle, which relies on crying to filter out salt.

Previously, in order to verify the authenticity of turtles' tears that purify seawater, scientists specifically fed a turtle 3 liters of seawater.

Not long after, scientists discovered that a sticky liquid was flowing from the corners of the turtle's eyes. They quickly collected the liquid and conducted tests.

The salt content was surprisingly high. The scientists then extracted blood from the turtles and found no significant increase in the salt content.

This experiment strongly confirms the claim that turtles rely on tear glands to purify seawater.

The principle is that when seawater enters the turtle's body, the salt in it is carried away by the cells but is not absorbed. Instead, it accumulates near the tear glands, dissolves with the tears and is excreted.

The purification ability of sea turtles makes humans marvel at the wonders of natural species.

If the example of the turtle can be called magical, then the next one can be called bizarre, it is the shark.

Fresh water with a "flavor"

You may have heard that although shark fin is a delicacy sought after by the rich, shark meat has a smell of urine, so many unscrupulous hunters throw the sharks into the sea after cutting off the fins.

In fact, the smell of shark meat comes from the process of purifying seawater.

When sharks defecate, urine is not excreted from the body, but accumulated under the skin of the body.

When sharks grab seawater through their body surface, the salt cannot enter the shark's body due to the osmotic pressure difference between the urea in the cortex and the seawater.

The composition of the cortex and urea acts like a natural water purification barrier, allowing sharks to replenish water anytime and anywhere.

Of course, urea accumulates in the shark's cell tissue for a long time, which also makes shark meat smell pungent and the meat tastes extremely bad.

"Dry Rice" Supplement

This method of replenishment often occurs among marine carnivores, who replenish their needs for fresh water by eating the water in their bodies.

Land creatures also have this habit of replenishing water. Lions living in Africa rely on hunting medium-sized herbivores to obtain water. Therefore, they do not need to replenish water frequently during the dry season.

This is particularly evident in marine life.

For example, the blood, eyeballs of fish, and the water in the spinal cord and cells of marine vertebrates are all important sources of supply for predators.

For whales, due to their large size and high demand for water, it is impossible for them to rely on their internal organs to purify water all the time.

You should know that the blue whale is 19 times the size of a human. Humans need 8 glasses of water a day, and a blue whale must consume at least 150 glasses of water.

Where does so much fresh water come from? At this time, the fish and shrimp swallowed into the stomach will replenish the source of fresh water for the whale, thereby reducing the purification pressure of the internal organs.

It is worth mentioning that this method is also an auxiliary means, and more fresh water sources must rely on their own purification capabilities to solve the problem.

Magical Bird

Although seabirds are not marine creatures, they often fly over the ocean and are accustomed to drinking seawater.

Seabirds purify seawater in the same way as turtles, but they expel substances containing salt crystals through their nostrils.

Therefore, seabirds have stronger purification capabilities than turtles, which enables them to fly for long periods of time at sea.

The species in nature are wonderful and diverse, and there is no reason not to protect them.

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