Experienced sailors all know that if you are unfortunate enough to capsize and fall into the vast sea, then even if you are thirsty, you must never drink the water in the ocean, otherwise it will aggravate your death.

This is because the water in the ocean contains a high concentration of nitrogen chloride and other minerals. The concentration in seawater is higher than that in human cells, so that when we drink seawater, our body not only cannot replenish water, but also makes us The body exacerbates the loss of water.

Humans can avoid drinking water in the ocean to preserve water in the body, but marine life is surrounded by sea water, how do they drink fresh water?

For marine organisms, they cannot directly use seawater, but in the process of evolution, they have evolved corresponding strategies to solve the problem of high seawater concentration. Among them, different creatures have different strategies.

gills

For freshwater fish, they do not need fresh water at all because they live in a freshwater environment, and their body fluids are more concentrated than freshwater, which causes freshwater to be replenished to freshwater fish by osmosis .

Freshwater fish also consume a lot of water when they ingest algae, plants or other fish, and they do not need to sweat, so the water in the body is sometimes too high, causing the cells to "stretch". For this reason, they sometimes It will also drain out.

Unlike freshwater fish, seawater fish must drink water to replenish water. In order to obtain freshwater in seawater, they have evolved a method of desalinating seawater, which is to desalinate seawater through "chlorine secreting cells" in fish gills. .

Although teleost fish can metabolize some salts through their kidneys, they mainly pass through chlorine-secreting cells in their gills, which filter seawater, allowing fish to obtain desalinated water.

Urea

Although sharks live in the ocean, sharks never drink water, and their method of obtaining water mainly relies on "urea" . Most organisms quickly excrete urea, but sharks are an exception. Sharks have a special mucous membrane that allows urea to be stored in the body, which is why shark meat smells bad.

Due to the existence of urea, the osmotic pressure in shark blood is much higher than that of seawater. Under the action of osmotic pressure inside and outside the body, seawater will flow from the outside to the inside of the body through osmosis, so the shark does not need to drink water. Of course, sharks also excrete salt through their salt glands, more on that later.

marine mammal

Marine mammals, like terrestrial mammals, also depend on freshwater resources to survive. And they can't store urea to increase the osmotic pressure in the body like sharks; they can't filter the salt in the water through the gills. In this case, how do they get fresh water in the ocean?

The way marine mammals obtain fresh water is actually very simple, that is, through food. Marine mammals live in seawater, they do not need to sweat to regulate their body temperature, and they do not lose water by evaporation from the sun, so they have less water requirements and can supplement from the food they eat.

sea ​​turtle tears

If you look closely at the turtle, you will see that there are often tears in the corners of its eyes, as if something unpleasant has happened.

But in fact, it is a very natural phenomenon for sea turtles to shed tears, and the tears they shed are not ordinary tears, but liquids with high salt content.

Turtles are reptiles, and their kidney function is not as perfect as mammals, so they cannot metabolize salt in the body through the kidneys. But behind their eye sockets there are glands that expel salt, also known as "salt glands" .

The salt glands of sea turtles are very developed. Researchers once injected seawater equal to about 1/2 of its body weight into the stomach of sea turtles. After 3-4 hours, it took in more than 90% of its body and absorbed it. The salt is excreted from the body through the lacrimal gland.

That is to say, there is a "desalinator" inside the turtle's body, so that even if they ingest seawater, they can still obtain the fresh water they need from the seawater.

In fact, not only sea turtles have this skill, many seabirds and reptiles also have salt glands, and they are all able to drink seawater directly in this way.