uh, here is a site someone gave me a while back in a forum. it's about goldfish but the symptoms should be the same on any other fish.
http://www.goldfishinfo.com/ailment1.htm#anchor
I wouldn't medicate before they get sick....there may be something you can put in there like stress coat(?) that will keep them from getting stressed out to much and then getting sick as a result.
As far as looking for healthy fish, just make sure they dont have white spots on them, torn fins, swim funny (funny as in unlike other fish of its type...). I wouldn't get a fish from the same tank as fish you can tell are sick or dead....unless you want to try to nurse it back to health or something...because it may wind up looking like the sick/dead fish before too long. Oh, i would be careful about fish from Wal-Mart.
Oh yeah, dont get a bunch of fish at first.
To have a better chance of your fish not getting sick on down the line, make sure you do research on the type of fish you want before you buy them...or ask about them on here. They can get sick from the wrong water conditions.
And don't forget to change your water.
I know i mixed up the answers to your questions, oh well....i hope that helps anyway. I am not 100% sure on all of that stuff, like the stress coat for example. I would make a seperate post, if no one clears it up on this one, before you use it. Goodluck!
