why are dolphins and other sea mammals able to deal with seawater whereas any seamen would rather die of thirst than drinking only one cup of saltwater

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What is there essential difference? Is there some kind of filter and if so, where and how does it work?
And what about other fish? Do they employ the same mechanism? And seaweed and stuff?
My basic understanding of living cells says that much salt does much harm, therefore as far as I’m concerned, there should be no living cell in the whole wide ocean.
Also interesting: how do eg salmons perform the transition between sweetwater river courses and their long mating routes across the ocean?

In: Biology
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I don’t know the specifics, but ocean life have glands to “remove” the salt, meanwhile the “rivers life” doesn’t.

There is not much research on this so good question

Their kidneys are super cleaners compared to ours.

Also scientists say they get their water from the food they eat…. this is debatable as many whales migrate long distances and food is not always readily available.

Although it’s literally all water, many of the animals in the ocean treat it a lot more like a desert.

The water is too salty to ingest in large quantities, and it’s constantly trying to dehydrate your tissues through osmotic pressure. The struggle in that environment isn’t really that different from a desert animal.

So like a desert animal, fish and oceangoing mammals must conserve their body moisture and source new water from their diet instead of from the environment. They expel most of the saltwater they ingest when eating, and have very powerful kidneys to deal with the rest.

The mammals have different physiology to us humans, essentially.

Our digestive and other systems need salt, but there are limits. Too much causes problems. Too little also.

Marine mammals actually actively try not to “drink water” like many carnivores they get most of the water they need by eating other animals (fish), their kidneys *are* more effective at processing the salt water, but for the most part that simply means the salt is passing through their urine rather than being absorbed into their bodies. There is actually is plenty of detailed information on this, here are a few more sources [Scientific American](https://www.scientificamerican.com/article/how-can-sea-mammals-drink/), [NYTimes](https://www.nytimes.com/2019/05/28/science/marine-animals-salt-water.html), [The Conversation](https://theconversation.com/curious-kids-how-do-sea-creatures-drink-sea-water-and-not-get-sick-110979).

*You asked about mammals specifically, but interestingly sea birds and sea turtles do have a whole organ that is primarily used to process (and excrete) excess salt from their blood called the* [*supraorbital gland*](https://en.wikipedia.org/wiki/Supraorbital_gland)*.*