Nothing like a dolphin, but there's a fish called an elephant nose that kind of resembles one, I guess.
http://www.liveaquaria.com/product/prod_display.cfm?c=830+836+1882&pcatid=1882
They're wild caught, and should only be bought by those experienced though since they're very very sensitive, easily catch diseases, and are scaleless so you can't use most medications with them.