Salt water fish vs. fresh water fish

[MaggieTheCat]

I started doing a little research on this, and realized that I don't really know what to search for in Google. What I want to know is the difference between salt water fish and fresh water fish, ie, how and why some fish survive in salt water but not fresh, and vice versa. As a bonus, I'd like to figure out how some fish (I think salmon?) can survive in both fresh and salt water.

I did a basic search for "salt water fish" in Google and got a lot of results about buying salt water fish and setting up salt water aquariums and whatnot. So does anyone know anything about this, or at least have an idea of how I can do a search to get the results I'm looking for?

[Broomjockey]

Salt water is more buoyant, so the smaller swim bladders won't let it float in fresh water. Further, the cells in each have different tolerances for the amount of water moving in and out of their cells due to solute in the cells/water.

Why can salmon? They evolved that way. They just really have greater tolerances. If you want sources, hit wikipedia and use the citations and further readings links at the end of articles.

[Food Lady]

try googling "studies on saltwater fish and freshwater fish"

[Spiffy McMoron]

Why can salmon? They evolved that way. They just really have greater tolerances.

This.

There are a million different things that can affect an animals ability to survive in an environment. Using the example of fish, salinity of the water isn't any different than depth/water pressure, water temperature, O2 levels, etc. Some fish are incredible adaptable to different environments (like the salmon) and others aren't.