Hello all,
You can't lump all triggers together and start making blanket statements about how safe a given fish will be with them. They are not all the same. There is the undulatus which will bully a fish that is 20 times his size. That's not an exageration either. :roll: I had a 3" undulatus beat the crap out of a grouper the size of a football. You literaly can't keep them with ANYTHING.
Then you have the niger which can be kept with almost anything without fear. Most other triggers fall somewhere in between. Most triggers in the Rhinecanthus genus are fairly mellow, and can be kept with damsels, angels, and more robust clown species without any problems. They should be added last, and they should be small. There is always the potential for problems as stated above, but as a whole, Rhinecanthus (huma huma, rectangulatus, etc) are good choices. Nigers, crosshatches and bluethroats all do well with other fish. If anything, they are shy.
Clowns become aggressive with age almost without fail, and almost always end up needing their own tank. A queen trigger? Forget it. They get HUGE, with destructive habits that match their size. This brings me to a point about the Rhinecanthus triggers, especially R. aculeatus - the huma huma or picasso trigger. They don't grow! Well, the grow, but they grow very, VERY slowly. Don't purchase a juvenile thinking you're going to end up with a nice large adult in a few years. In 6 years you will be lucky to have a 7" fish! This is a positive attribute about this species though, it makes them great aquarium candidates as opposed to other species which grow large quickly like queens and nigers. They will also do fine with damsels of course.
Hope this helps.
Cheers
Jim