Aggressive Female Swordtail?

Question
Mkay

Background info:

So my little brother and I both have a ten gallon tropical/freshwater tank. They are both 10 gallon and several months old.

Over the past few months, he had deaths in his tank, including a few tetras and an otocynclus. I bought him a yellow mystery snail, but he managed to kill that as well!

I checked his water and went to go stock up on some new fish and some water balencers (His water was incredibly hard, so I also bought him some driftwood).

So right now he has: 5 tetras, a goldfish, a male and female swordtail and a  bottom feeder that I forget the name of. They were perfectly fine yesterday when I added in the swordfish and the bottom feeder, but now the female is aggressive...

The problem:

Today I was watching the tank and the female swordtail was nipping at the poor goldfish! I thought at first it was playful, but the goldfish seemed more distressed than playful, so I tried tapping the glass, but she kept going back and attacking him.

I sectioned her off in a breeding net and the goldfish seems relieved but I was wondering why she could be doing this?

She was eating fine yesterday, but I tried dropping in a little food for her after I put her in the breeding net (because I thought she was perhaps angry out of hunger?) but she didn't touch it.

Any advice or reasoning as to what the problem could be?

Thanks.  

Answer
Hi Sara,
Wow, I'm sorry to hear that.

Sounds like you may have to move the swordtail into a separate tank of her own (Or take her back to the petstore :(

Sometimes these fish do tend to nibble on goldfish (due to their slime coat) and I don't think things will improve much on that. Swordtails have a natural "picking" foraging behavior that they may employ on larger fish.  She herself is probably stressed from the isolation in the net the reason she isn't really eating.

Sorry for the bad news.

Hope things straighten out!
Karen~