Swordtail dorsal fins

[shaela21]

I have 2 female swordtails in a 20 gallon tank along with 6 rainbows, 2 Cory's and 1 plecto. I noticed today that the dorsal fin (the one on the back middle, the largest one) has some nips taken out. This is on both of them. I have never noticed this before, and the other fish seem fine. Any comments or recommendations for this. I am still fairly new to this aquarium thing, so I am concerned. Ph=7.6, alk=0, nitrates=0, gh=4 degrees, and kh=3 degrees.
Thanks

 

[webmoose]

what kind of rainbows?

 

[shaela21]

There are 3 Celebrese and 3 Praecox Rainbows.

 

[webmoose]

not sure about the celebs but i wouldn't really suspect your praecox.

 

[Menagerie]

I wouldn't worry. It could be that the two females got annoyed with each other and nipped. I never see my celebes nip, but it could happen.