Hehe quite impossible unless using Biotech to infuse them sperm & egg. 1st of all the reproduction method is totally different. Guppy is livebearer and tetra is egg layer. 2nd the reproduction organ. Because of the diff. method, they have diff. organ esp. on the male. The guppy male has a gonopodium whereas tetra doesn't (I pressume no third leg sticking out ) . Even if you artificially extracted the sperm, it doesn't recognise the egg of the diff. species. So artificial insemination will not work. So the only choice is Biotech by infusion. BTW not recommended, I wouldn't want to create a killer guppy strain .