short answer is yes they are quite aggressive when larger, most people find that once they hit 6-8in they dont get along with very many tankmates anymore and can be persistant with picking on fish they dont like. that being said my argentea that I had was almost 8in when he died and never had any issues with being overly aggressive, he could hold his own just fine but never started fights with anyone, but from previous threads i have started and others i have read through this is the exception and not the rule for when they hit this size, some people have luck with keeping them with smaller fish that dont pose a threat but most people find they dont work successfully with other larger cichlids in the long run, I am not saying it is impossible by any means just that it may take a turn for the worse once the arg gets larger