In general salt water aquariums are populated by those fish that stay in the tropical coral reefs. Some like the Surgeonfish are shoaling fish, meaning to say they prefer to move in large numbers, so if bought on their own tend to pine and die from being lonely. They appear to be continually feeding as they like to enjoy their day scrapping algae from the rocks. If you plan to house such fish you should buy an ultra violet water sterilizer because they are vulnerable to disease.
Butterfly fish are firm favorites with lovers of marine aquariums not least as they are great to look at. They are hard to keep however as they demand top quality conditions and therefore are not the fish to purchase if this is your first attempt at running salt water aquariums.
Some fish like the Triggerfish can be very aggressive specifically in the limited space of a fish tank. This doesn't stop people buying them though because they are stunning to look at. They require handling carefully as they can bite their owners if they sense they are not being handled with respect!
Mandarin fish are spectacular but should never be housed in a fish only aquarium tank as they will gradually starve to death. They like to nibble on microbes found on coral and living rocks and demand excellent water quality. They work well with other species as other fish have a tendency to leave them alone as they will release stinking mucus if they feel threatened.
Puffer fish in many cases are purchased because of their uncommon looks. These fish need careful handling not least as their teeth and spines will keep growing and need to be monitored by a trained vet. Otherwise they will starve to death.
It is crucial that you understand all of the different requirements of the inhabitants of salt water aquariums if you want your colony to flourish.