I don't mean to sound mean or any thing, I just appreciate the science behind such behaviours.
Fish in the wild also defend their territories against males of the same species sometimes; interesting to see if bullies also use sight to differentiate between the sexes in their species. Interestingly enough some fish (i forget the name, it was in my old biology book, it had red on it) recognised not only body shape; but also the where the colouration on the dominant male was. the males are aggressive towards each other, to defend their territories - but the males only went for the correct fish based on the body shape of the fish, and the location of the red patch.