No, platies are not aggressive. They rarely exhibit aggression towards their tankmates. Platies are peaceful and non-violent, making them a wonderful addition to community tanks. They also get along well with various other non-aggressive species, such as mollies, guppies, and more.
However, in certain situations, male platies may exhibit aggression towards other platies. First, as livebearer fish, male platies will always want to mate, causing them to harass the females constantly. This isn’t exactly aggression, but it can stress out the females, so you should keep a 2:1 ratio of female to male platies.
Male platies may also show aggression towards other males to assert dominance, especially if the tank is overcrowded. Additionally, they may sometimes fight over food and mating privileges as well.