Having studied all aspects of the problem, pundits found that fish do not drink the same way. It’s even better to say - they don’t drink, but get water into their body. After all
fluid is involved in all metabolic processes. Without it, life would not have been possible. That's what they did.
Freshwater inhabitants
These beauties in their body have so many salts that they do not need to swallow water to ensure metabolism. It turns out that they drink fish with their bodies, not their mouths. Schematically, the process can be represented as follows. If you place two liquids next to each other that differ in the concentration of salts dissolved in them, open the valve, then where will the diffusion vector be directed? Correctly, towards a more saturated liquid. The greater the concentration of salts, the greater “thirst” torment. Water begins to move towards a saturated solution. Fresh water contains a small amount of additives, its osmotic pressure is almost zero. And in fish - on the contrary. There are a lot of salts in their body. It turns out that they constantly absorb the environment. And their main task
is not absorption, but excretion. This process is established, otherwise the freshwater inhabitants can swell and burst, so great is the flow inside the body. It turns out that the fish drink in a very original way. They absorb liquid for their own needs, and even regulate its pressure inside themselves.
Marine inhabitants
For these inhabitants of salt water, the process is the opposite. In the sea, the salt concentration is high. The osmotic pressure index is thirty-two atmospheres. Sea fish drink continuously. They simply have to constantly replenish their reserves, because the environment constantly “dries” them, water seeps out through the whole body. The fact is very comical. When sea fish drink water, they are alive and well. Stop - they can “dry out”, die from loss of fluid. And this, being constantly in the water! But these are the laws of diffusion. The osmotic pressure inside the fish bodies is only ten to fifteen atmospheres. Outside - more than twice as high. So poor fish have to drink continuously in order to survive and not “dry up”. It is interesting that for life they need fresh water. They “filter” it, removing residual salts through the gills. For example, crocodiles can do the same. They remove salts through
lacrimal glands. When the crocodile eats sweetly, he cries. This excess salt is released from the body.
Sharks and stingrays
These inhabitants of the oceans were singled out in a special class. The reasons for this “biased” attitude are that the mechanisms of their relationship with the environment are very different from other inhabitants of the deep sea. These fish do not drink as much as the rest. They “learned” how to handle the difference in osmotic pressure differently. They retain urea in their circulatory system, although this is very harmful. These creatures even have a special shell in their gills - protection against excess salts. Thus, stingrays and sharks maintain an internal concentration of salts higher than in the surrounding area. Scientists believe that this is an indicator of the antiquity of these inhabitants of the seas. They, like freshwater, absorb fluid throughout the body.
Why fish can't live in any environment
The difference in the mechanisms of interaction with liquids does not allow them to master the entire space of the oceans. Those who feel good in fresh water will die in the sea. And vice versa. There are exceptions to this rule. So, everyone knows well that part of the fish lives well in salt water, and reproduces in rivers. That is, they are diadromous - they can live in any environment. Whether the fish drink water in this case depends on the state of the surrounding fluid. They feel by the body in which direction the process has moved, and in case of need they begin to consume water. Their internal organs quickly
rebuild to the environment. For example, salmon, pods, sturgeons, and some other fish are diadromous. While they splash in the sea - they drink the same way as all its inhabitants. When sent to spawn, their gills quickly adapt to the environment. Therefore, they do not die from the transition to water with a different concentration of salts. The reverse process occurs in the body of their fry, when they descend into the natural habitat - the sea.
