Mine established their pecking order in 2006 and its never changed. So almost no fighting.
The largest is 117cm the other two are 90cm and 100cm. They will not be growing anymore so it will probably stay this way.
The only fish that can but don't fight with the big Phracto are the 2 Wallago's as they also established a truce with it. The Wallagos do fight with each other with the female beating up the male most of the time. However the male does leave some big scars on her the odd time. The 275cm water depth and the L shape of the tank combined with the 122cm high wall which blocks lines of sight, really helps reduce aggression.
This is the female Wallago leerii. The arapaima is 183cm long and swimming about 450 cm behind the Wallago.