I was trying to read about why freshwater fish die in saltwater but it was still a little confusing to me.
In: Biology
A living cell is designed to work at specific conditions: the chemicals that make up a cell perform best at certain temperatures, with certain concentrations of chemicals, etc. This also applies to how much salt is in the cell: living things need a certain amount of salt in them in order to survive. Even if the amount of salt inside the cell stays the same, the amount *outside* the cell also matters: if the fluid around the cell is saltier or less salty than the cell itself, the cell can dangerously shrink or swell as water flows through the cell’s membrane toward the saltier side. Living things have different ways of keeping the right amount of salt in their body, but they’re tuned for the environments they live in. For instance, humans’ urinary systems help keep the proper amount of salt in the body if they eat or drink most things, but they’re unable to get rid of enough salt to survive if a human drinks nothing but seawater. Similarly, most freshwater fish aren’t suited for keeping salt out of their body if they swim in sea water, and most salt water fish can’t keep enough salt *in* their bodies if they swim in fresh water.
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