The way that we breathe air and drink water, is extremely different to saltwater animals.
Saltwater animals, breathe air, like every other animal, but can only live in saltwater environments, same goes for freshwater animals, but anadromous fish are a different story.
A type of fish that is anadromous, is the very well known Salmon.
Salmon are born in freshwater rivers, then move to the ocean (saltwater), they then go back to the freshwater river to reproduce with other salmon.
But how do saltwater fish live in salt water, or Salmon live in saltwater? Well, the animals in the saltwater environment use a process called, osmoregulation.
Osmoregulation is a process that can let them control the amount of salt and water allowed in their body.
Saltwater fish drink a lot of water obviously, so they have this extra salt left in their body. And the extra chloride ions are then removed by active transport, and then leaves the body by animals kidneys or gills. And since sodium ions are attracted to chloride ions, it follows then follows it outside the body.
In the case of freshwater fish. It’s pretty dangerous if they drink excessive amounts of water, so they either drink little to no water at all. And they urinate huge amounts of liquids. And instead of gain the salt from the water, they gain it from the food eat.
Now for salmon, it’s very different since they live both in freshwater and saltwater. If they’re in freshwater, they do exactly the same as other fish do, they urinate a lot and get salt from food.
But if they’re in the ocean, they produce plentiful amounts of cortisol. These cortisol starts growing chloride cells. And once there’s chloride cell ejects other chloride cells, the salt will follow the chloride.