Sex Change and Social Awkwardness

So this week we noticed that one of our 'female' swordtails is sporting a sword at the tail, which only the males have.  This has created some social awkwardness in the tank, as the established male who thought he had a harem of 2 females now is afraid that he has competition for 1.  So there seem to be more confrontations going on now.

You learn a lot of weird stuff with this hobby, and while a lot of fish can change their sex, there seems to be some debate as to whether in swordtails it is truly a female changing to male, or if it simply was a male all along that was a very 'late bloomer'.  Some claim the change happens occasionally to females when they get quite old or when there aren't enough mates around.