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What happens to a freshwater fish when it's put in saltwater?

Okay, I've answered something similar before, except it was the reverse. Basically, osmosis screws the fish over. What is osmosis? It's basically a form of passive transport that draws water in and out of cells depending on concentration levels. Passive transport means it travels down the concentration gradient; so high concentration to low concentration. So if there is a high concentration of water inside the cell than outside the cell, then the water will flow outside the cell through aquaporins to achieve equilibrium, and vice versa.Freshwater fish, in their natural environment, continuously pee to get rid of excess water because of osmosis. There is more water outside the fish than inside the fish, so the fish absorbs water into its body via osmosis so equilibrium can be achieved. If the fish doesn't keep peeing to rid water from its body, its cells will explode and will die.On the other hand, saltwater fish adapt to their environment by continuously drinking to replenish the lost water in their bodies. Because there is so much more salt outside the fish than inside the fish, water is constantly drawn from the fish to try to achieve equilibrium.In summary, in their natural habitats, saltwater fish drink, and freshwater fish pee. Just remember that.Now (don't actually, I swear to God—) put a freshwater fish into a saltwater environment. Remember that in a saltwater environment, water from the fish is drawn out. A freshwater fish's adaptation is continuous peeing. What does that mean? That even more water will be lost from the freshwater fish's body!If you're still a bit iffy, let me put it like this. Imagine that the environment draws out 2+ water from the fish, and that peeing releases into the environment 4+ water. Add that together and you have 6+ water escaping from the fish.In conclusion, the fish will die from dehydration. It will lose all the water in its body and become an aquatic prune.