I kept a pair of motoro in with a large pair of lenticulata for quite a while. They did OK together but every once in a while the male pike would just nail the rays and take a chunk out the disk. I ended up getting rid of the rays because they were just getting beat on too much for my taste. It seemed like just as the ray would heal up the pike would nail it again.
yeah it's funny how a big tank will do so much----I saw a beutiful public aquarium that had pikes mixed in with rays and ....a flock of discus! What a gorgeous combination of shapes and colors