@lonelygod - Whatever you don't put the rectangular trigger fish in a tank with other salt water fish if you want them alive. The trigger fish can be quite aggressive and is likely to kill a foreign species.
On that note, they actually do make good pets, though you will need a rather large tank to house one. My trigger fish are in a 100 gallon tank and I have three now. The key is to get them when they are small and to confuse the other trigger fish when you add a new one to the group. Just move the rocks around a bit and they won't even notice their newest member.