Hard to say - my Red Tails current and in the past where very aggressive towards any fish - payara, cudas, arrowanas, cichlids, chalcues; most esp. each other. My yellow tails are more docile and nudge or nip - The Red Tails I've kept/keep can be down right relentless but I'm yet to see them kill for thrill with another species other than their own. The Yellow tails are far more accepting of each other and shoal in various sizes.