also,aros are much better at maneuvering than gars...when you see aros spook out,in a big enough tank they easily turn around instead of hitting the glass straight in the face.
gars however,dont maneuver very well and easily break their backs by crashing into the glass.
especially with the kind of snouts they have...
another thing,IMO,is that aros tend to eat very aggressively and outcompete gars.
ive also seen gars become so hungry they start to outcompete the aros.
either way it leads to a difference in growth rate with one eventually much bigger than the other.