Back in the 70's I had a male and a female, bought separately. It was a big aquarium (510 gallons) and they swam, without fighting, pretty close to each other with the male behind the female. There was a half clam shell with scalloped edge that they would often go into and "do something." It would bounce and shake and then they would come out, uninjured, and continue cruising the tank together. I often wondered what they did in there.