if we may be so nosy, tell us more about your setup. what kinda equipment do you have? what substrate? do you have live rock? is it cured, uncured? i would say probably best not to do tangs in a 55 for any length of time but if you did, go with one that maxes out at a smaller adult length, like yellow or scopas tangs. if you want a picasso trigger, keep this in mind: (excerpt taken from scott w. michaels book Marine Fishes: 500 essential to know aquarium species) "Belligerence will increase with age, and they should be kept with fish equal in size or larger. if introduced simultaneously into a larger tank, they can be housed with members of the same genus. jeveniles are compatible with members of their own species, but fights are likely to become fore frequent as they mature. will occasionally bite heater butes and air line tubing and may rearrange aquarium decor." so you can imagine what they will potentially do to other fish who arent capable of holding their own, or hiding, in such a small tank. Maybe you could do a picasso, and a snowflake eel, and a lionfish. heck that might be too much for a 55 though. cant imagine itll be easy to keep clean! sorry if I wasnt much help :(