I have a few wild Peruvian "Altums" in a 30 gallon tank, and two hang around together most of the time, and keep the other two fish in the upper extreme sides of the tank. Not terribly aggressively so, but it's definitely noticeable. These same two fish swim together. I do see them display a tiny bit of aggression between them once in a while.
Do you think they could be pairing up?
Do you think they could be pairing up?