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

Question

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

Answer 1

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