Is their blood saltier than freshwater species? Is this also why saltwater animals die in fresh water? It makes sense to me why fresh water species can’t survive in saltwater but not the other way around.
In: Biology
Saltwater fish drink lots and lots of water to replenish the water the ocean (saltier than their body) takes out of them through osmosis. They pee out the salt. Freshwater fish don’t drink water, but their body sucks in water (less salty than their body) through osmosis the opposite way, and still have to pee it out. Seawater fish could technically live in fresh water if they could pee fast enough to get rid of all the water they take in from it. There are examples of fish that can live in both though, salmon and bull sharks come to mind
They have better and bigger kidneys than us (in proportions). Better kidneys means they use less water to get rid of the same amount of salt.
Kidneys take the salt out of the blood and excrete it with the pee.
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