And where are you pulling that information from? Seeing as there are about 60 different species, that seems like an incredibly blanketed (and untrue) statement. While yes, there are some feistier (and I use that word because its generally not true aggression, just territorial) species, like panduro and nijsseni, most are quite calm and passive, similar to that of mikrogeophgus ramirezi. Not to mention, any "aggression" put out by an apisto generally would not phase discus. With all that said, mikrogeophgus ramirezi tend to be my suggestion for a tankmate for discus, as their colors compliment them well