Hello,
I would agree with cain420.
Salt water aquariums are very delicate and very personal. You would have to have a knoledge of where your friend wants to go with the tank. While "most" fish wont have a problem with a mandarin, you will need to know a few other factors before commiting.
like:
what size is the tank
are there any inverts in the tank
will there be inverts in the tank
how old is the tank
what does he want in the tank???
its really not a suprise you can or should responsibaly make... however, by asking the right questions you may be able to get a specific awnser with out spoiling your intended suprise.
also, here is a personal story...
my grilfriend bought me a blue spotted puffer, (after finding out these questions) I loved him, but he died and brought internal parasites that killed off 3 other fish, there was nothing I could do...
its been about a year later and she still feel really bad about killing my fish even though it was really not her fault...
just something to think about. there is always a risk of "backfire"
you found a great site to help you out with this, just remember asking the right questions is the best way to make sure youve got your bases covered.
-oozy-