What are some species of salt-water, fresh-water, and both-water fish?

The only one I can think of is Salmon, hatches in freshwater, lives its life in saltwater, then returns to freshwater to drop off its eggs. But it dies shortly thereafter.

A friend had told me about a shark he saw in brackish water.
I’m sure there is more info out there somewhere on this ;)

@lucillelucillelucille

Your friend might have seen a bull shark.

The American Eel is a freshwater fish (?) that spawns in the Sargasso Sea, which is a bit northeast of Cuba.

Also these two come to mind
European Eel. Anguilla Anguilla
Sea trout. Salmo Cambricus

three-spined stickleback

Most people dont realize this, but both mollies and guppies can be acclimated over to salt water.

I used to keep mollies in my reef tank, they make excellent algae cleaners and are dirt cheap

Salmon. They’re born in fresh water, go out to sea to mature, and then they return to the place they were born to mate. I believe some species of trout do the same.