system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't saltwater fish survive in freshwater?
gpt
Because their cells have adapted to saltwater. If they were in fresh water the water would try to equalize the chemical concentrations of the fish's cells with itself, which would involve flowing into fish cells and bursting them open. The same thing happens to people if we drink too much water.