Yes, I believe you all may be correct. I am hoping that he or she will get along with everyone in my 90 gal. I did a search on synspillum and it says they can be semi-aggressive with their own kind and that they should be kept with similar behavior fish. It seems the bigger he gets the more dominant he gets in my tank. My 4 in Acara and him have had several "stand offs" but the synspillum gives in and swims off to another area of the tank.