I think my female swordtail is growing a sword. The fish you see in this picture now has a darker bottom edge of her tail. My other female has a darker upper and lower edge on her tail so I thought it was normal at first, but now it appears to be coming to a point. You can see in the picture the fin was nipped, it was this way when I bought her. If she were a male that might explain why the other (smaller) male kept getting sick up until his death. There were only ever 3 fish in the tank, so 2 males and 1 female could have started some feuding. This is all speculation at this point, but is there another way to tell other than the sword? Is it possible for a female to have a small colored point on the tail? I'll get a picture of this new development to you as soon as I can.