As you can see .. oscars and red hooks with a Royal knife in there .. they all get along 99.9% of the time .. the O's might be a pair .. i dont know how to sex .. but they have been together since around 1" and lived in the 55 gal then moved to the 120 that they are in now .. the red hooks and royal where picked up at the same time as the O's so they have been a family for a while now .. they will all move into the 150 gal tank when the new ray tank is set up (in the future)