I have a few swordtails (so I can have some little itty bitty swordtails for an occassional snack for the polypterus) in a tank with some bolivian rams. I just noticed one of the female swordtails has begun emulating the ram behavior ...and is ramming the largest ram (which is about 1.5 times the size of the swordtail). I just thought this was quite funny that a "peaceful" fish was taking territory away from a "semi-aggressive" and larger fish.