What would be the best tankmate for a baby(5 inch) arowana?
Out of these: oscar fish, sun catfish, pictus catfish
Out of these: oscar fish, sun catfish, pictus catfish
Brian already told you in the other thread, your aro is way too small to be housed with any tankmates at this point.
Thats the whole point why you dont get a tankmate when you have a 5" arothe pictus is armed with twice the amount of spines and has poison on each spine in their fins.

keep him alone until you have done proper research and care for him some. they are fragile fish when small.