will be very tough on the guppies. They aren't very closely related. Why don't you try crossing horses and cats?
How do you know that the female Gambusia (Gambusia means worthless in one of the languages supplying the term) was NOT pregnant. Is she more or less an adult? Did you wait six months to see if she would drop? Did you give her lots of plants in a 10-gallon tank and almost unlimited live or rinsed frozen food when she was big? Are you sure that she has not dropped and eaten her fry. I've had a female G. affinis for a year and a half now and have no fry to show for it. I'm quite sure, from her changing figure, that mine has been dropping. I have other uses for my tank space than for her fry.
Male guppies, as you mention Josh, would try to mate with most anything - even each other and that Cory. That still doesn't mean that they will be successful.
Was it you that confused guppy and Gambusia fry before? What was suggested then?
I know that all sounds very uncharitable but we've been around and around on this on GL. You are probably wasting your time and maybe the lives of the guppies.
And why would you confine them to a breeding box where she can more easily shred or even kill all three of them? In the case of the often very large Gambusia females, you may actually want several male Gambusia per female or at least want give them lots of hiding space and places. People may thoughtlessly bag a male and female in the same bag for an auction. We all get too much in a hurry. But while they may still be a pair at the auction, the buyer may arrive home with only a female still alive. And the guppy males are not likely to be more combative than the Gambusia males.
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