What can some fish do that other fish long ago couldn't do?

Because saltwater fish can only breathe in saltwater (as in the ocean) and freshwater fish can only breathe in freshwater (as in tap water.)

In nature, most males are the colorful one and the females are not as colorful. (not as pretty) Why? Because the males want to attract the females and mate. If you look at a peacock the ones with the...

Not very long,because they are territorial.thats why your supposed to put the Betta in the tank last,so it wont do that kind of stuff.

It depends on what you say on getting along. Sometimes males will fight other males over a female and sometimes they may feel to cramped in their tank. If a fish is chasing another and tearing up the...

yes they do so they can live and sometimes that's how they survive