crossbreeding?

[DiverDown]

I have a live bearer tank that I started a while ago. I had a male and 2 female fancy guppies, and a male and female velet swordtail pair. After about 2 weeks, I was looking at the tank and saw a small yellow fish swimming around. I got excited because I figured my guppies had bred and one of them actually survived. About a week later, I found a few little red fellas swimming around. HUZZAH, my velvet's had bred as well.

Now, my fish are over a month old, and the baby "guppy" is developing a swordtail of his own. There is also a line of red dots down each side along the lateral line. None of my guppies have red in them.

Can guppies and swordtails cross breed? I thought they were of completely different families.

 

[Toirtis]

They cannot hybridise, however, swords and platys can, and guppies and mollies can.

However, guppies have been known to store sperm for many months...it is possible that the spawn you are observing were sired by a fish back at the shop at which you purchased them.