with respect to corals, I've never heard of anyone even thinking of breeding them in a captive environment. All we're doing is testing wild corals out, then keeping and spreading the one's that adapt and do well in the environment we provide.
We do try to make our tanks as much like the natural sea as possible, but we honestly don't get as close as we would like to think.
It's possible that some day in the future, we may end up using the corals we have in our tanks to repopulate the oceans reefs with some success. We're basically picking through all the wild corals and finding the one's that are most hardy and adaptable.
With respect to fish and breeding. It's not so much evolution that occurs, it's purposeful breeding for specific traits. It occurs much much faster than evolution, because we purposefully combine specific genome's to get the desired results. As a result, we end up getting the desireable traits quite quickly, however we sometimes get undesirable traits just as quickly. We might be producing the most beautiful and hardy Angelfish ever, but we don't realize that we've also ended up with some kind of nasty trait like extremely weak immune system, or weakness to a specific disease.
This sort of thing has happened with all kinds of domestic animals. Dogs, cats, cattle, sheep, nearly every domestic animal out there. The big difference between fish and most of those other animals is the speed at which generations pass. A dog breeder for example, might be lucky to go through a full generation per year. Depending on the species of fish, you might go through generations much much faster than that.
When actual geneticists (sp?) get involved it gets even crazier, because you don't have to wait for a generation to develop, see if they have the traits you're looking for and then choose the right specimens to breed. Instead, you can just look through the microscope, find the traits you're looking for, or verify that the next generation has what you want, and move forward. We're not even talking about actually tinkering with the DNA at this point, I'm only talking about looking.
Very cool stuff! Who knows what the future may hold, a quick change in the global environment might wipe out the fish/corals that can't adapt quickly enough, it may be the aquariast to the rescue, since we've found/bred the most adaptable and hardy corals and fish.