Today I just bought two swordtails to put into my "male" tank.
I have two tanks, a male and a female, as when I first bought my fish the store only had female guppies. About a month later one popped out a baby, and a few weeks later a few more arrived. Two turned out to be male, so wanting to avoid more breeding, I bought a second tank to separate the boys from the girls.
Today I thought that the male tank looked a little empty, only having three male guppies, a blue dwarf gourami and a platy, so I bought two orange swordtails. After putting them into the tank the male guppies started dancing- the way male guppies typically fight- against the swordtails, then the smallest, which was a quarter of the swordtails size began "pecking" at one.
So, not wanting to stress out the new fish too much, I went and moved them to the female tank, thinking that the female guppies wouldn't feel threatened by the new swordtails. I was wrong. The females started all out attacking the swordtails, trying to eat their tails and just ramming into them at full speed!
I have never seen guppies do this, it was extremely aggressive. In the female tank there are also several neons, which have never been attacked since introducing them. There are also a few guppy fry in there as well, and all the fully grown guppies just ignore them.
Is there a particular reason as to why the guppies might attack swordtails, I have read that they are supposed to get along great in aquariums?
Any advice is welcome