Strange Sword Feeding Behaviour

[darklight]

Hi, I have recently acquired a tank full of about 12 or so (what look like) female swordtails. At least none of them have developed swords. They range in size from 1cm to the main girl, who is 3-4 inches.

When I feed them, they start darting all over the place, grabbing food, obviously quite excited. But the biggest of the bunch spends most of her feeding time nipping the anal fins (or around the bum area) of one or two of the smaller swords, ONLY ever the black ones (she is mostly black too). Also she does the same thing to a solitary unidentified barb in the tank.

The other fish look mostly unaffected by this, but sometimes when it is happening the smaller black sword looks like it just gives up, and floats on its head being pecked, until the bigger sword darts off to bother another fish.

The upshot of this behaviour is the big sword misses out on most of the food, hunts around for a bit then just comes to the front of the tank to ask "where is my food?"

Can anyone explain this strange behaviour?

 

[kribensis12]

I think she is just showing dominance.

 

[darklight]

I noticed last night that it is just one that is being picked on - slightly fat - possibly pregnant? I also noticed both of the other black swords picking on this one - same behavior, almost like dogs sniffing other dogs bums.

I'm only worried because it is mainly the one fish getting picked on, and also it looks like the big fish misses out on a lot of food.

Do swords group together according to colour? It seems this way - I have roughly 2 of each colour combination / pattern, and they generally hang around with their matching partner.