JD's aren't as agressive as everyone makes it seem... my JD is the b*tch in my tank and he's about 4" while my blood parrot is the leader of the tank (4") and then my isletas(6") just hides.. but my JD just likes to fight his reflexion and eat. i would say that combo would be fine but the oscar will grow fast. as for the person above me^^ an oscar jag and JD would work but it all depends on tank size...