Poor little chap 
Unfortunately you never know how aggressive a fish is going to be, being wild caught might add to the aggressiveness of the diadema. Because they are rarer than other acara/aequidens species, you dont have as much information on their personalities, I would guess its more closely related to the rivulatus (Gold Saum/GT) than a Pulcher.
Combined with the HRP, together they obviously over power the other fish.
Unfortunately you never know how aggressive a fish is going to be, being wild caught might add to the aggressiveness of the diadema. Because they are rarer than other acara/aequidens species, you dont have as much information on their personalities, I would guess its more closely related to the rivulatus (Gold Saum/GT) than a Pulcher.
Combined with the HRP, together they obviously over power the other fish.