What we should not drink salt water we learn almost unintentionally when playing with the waves we take a drink (and we no longer want to repeat). This, in addition to being unpleasant, is dangerous at an organic level, but then a doubt may come to us: how do marine animals get hydrated if drinking salt water can be harmful?
From there we can also jump more doubts: do fish and river animals drink? Are the kidneys of marine mammals more like those of fish than of other mammals? As you might think, nature is wise and evolution has been forming systems so that all these animals can hydrate either by drinking or by pulling from other sources (never better said), so let's see how the smaller waters work these organisms.
Do the fish drink salt water? And fresh water?
Despite the accumulation of "curious" substances that the seawater of the beaches will have, for a drink we will not die. But what would happen if we were to drink salt water (speaking of one with 33 grams of salt per liter, like that of the sea) is that the concentration of salts in our fluids is much lower (9 grams of salt per liter of water) , and trying to equalize concentrations by osmosis the cells would release too much water shrinking, ending in extreme dehydration when trying to expel the salt with urine (demanding more water than ingested).
When trying to equal concentrations by osmosis the cells would release too much water shrinking, ending in extreme dehydration
Hence, the fluids of many marine animals have the same salt concentration as seawater. As they reminded us in Naukas, among them we find the bivalve mollusks, echinoderms (starfish, sea urchins), sponges, anemones and many others, all of them capable of having a "you to you" concentration and avoid dehydration.
However, others whose design has not been refined so much in this sense although it seems quite the opposite: the internal fluids of marine teleosts (and other groups) have a lower salt concentration than that of seawater.
Tele ... What? Teleosts, which groups most of the sea fish group. Thus, although they live as fish in the water literally hakes, breams, eels and other species require special maneuvers to avoid dehydration to drink seawater.
What is your trick? Avoid the absorption of salts (of all) to keep the water, expelling them to the outside. The salts that are not absorbed remain inside the intestine along with the rest of the unwanted elements of the food. From there they are expelled to the outside via the gills and urine, but to avoid dehydration they produce very little (and very salty).
In fact, they have kidneys quite different from the rest in terms of structure and functionality. The nephron is the basic functional and structural unit in a kidney; in the kidney of a vertebrate superior terrestrial (as we can be us, the cows or the cats, among many others) we see structures that we do not see sometimes in those of the teleost fishes, as the renal corpuscle (where the filtration is carried out) or the distal convoluted tubule (where filtrations are also performed), as explained in detail in this study by the University of La Plata (Argentina).
So, do the fish drink salt water? Yes, the sea people have to drink this water. But the thing changes for the river, whose concentration of salts in their body fluids is higher than the water in which they swim. Drinking would happen to them the opposite to us when drinking salt water: their cells would absorb water to equalize concentrations with the outside (fresh water), swelling until they explode.
| Do the fish drink salt water? Yes, the sea people have to drink this water, but things change for the river | What happened to the river fish was also clarified in Naukas, where they explained that freshwater fish have two mechanisms to prevent fresh water from entering: waterproofing and almost not drinking (only what is necessary to assimilate the ions that they need ). Even so there is water entry (some epithelial tissues can not be waterproofed by their functions), but these fish produce an important volume of urine, being the river animals that produce the largest amount of urine. |
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Do you drink marine mammals?
The teleost fish help the gills to eliminate excess salts, but what about the animals that inhabit the sea and do not have this specialized body? It is not well known how often marine mammals drink sea water, but the key again is partly in the kidneys.
The fluids of seals, whales, dolphins, manatees and other marine mammals have a concentration of salts similar to that of other terrestrial vertebrates (less than saltwater), ergo drinking seawater would run the risk of that dehydration that we explained. But if it is known that they drink, and there is also the part of salt water coming from food, what do they do to avoid it?
Evolution, as always, is "the fault". These animals developed a morphologically and functionally different kidney from a terrestrial animal (more nephrons in less space, called reniculated kidney), so that they can collect as much salt as possible and eliminate it with urine.
In this way, the urine of marine mammals is very salty (that of sea lions becomes 2.5 times more salty than sea water, as recalled in Very Interesting). And in addition to having adapted kidneys, what they do is try to drink fresh water when they can and the same as patients with hypertension: try not to eat excessively salty foods, as explained in Scientific American.
Very nice article you have there! But do not forget to cite your sources and credit your images when necessary
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