if you want them to get eaten, remove the rocks, because if one day the arowana decides that he wants to get them and he hide, the arowana will get hurt trying to get under or inside the rocks
the smaller one stays more dull
bigger one turns really red and ive seen it turn half red,same fish.
thing i see different is the bigger one has more of a hump on his head.
and the bigger one is a dancing fool in front of the smaller one.
would a male dance for a male? or f 4 f?
I have seen males dance to males. But usually the male will color up fully while the female doesn't. Plus the males tend to get bigger. I know nothing about the hump you talk about. So I still can't say for sure, but from what you describe I would tend towards a male and female.