New user here. I'm just getting back into freshwater tropical fishkeeping again after 10+ years away from it. My 9 year old daughter spotted a "baby fish" in our tank the other day, its totally unexpected and its got me a little baffled. The only live bearers I have are Guppies and Mollies, the only females are the Mollies. I know that they can crossbreed with Guppies but I've not noticed any of the tell tail signs of this. Now, my Mollies are both new fish so there is a possibility that one could have already been pregnant when I got her.
The confusing part is that there are only 2 fry that I have found, we found them 2 days ago, they are around 1 cm in length and seemingly happy in the hatchery that I went and purchased pronto! Today, I have noticed that one of my Mollies is starting to look quite big and boxy again (same one that looked this way before the fry were discovered). Is it possible that she only gave birth to 2 or so fry, she shares the tank with smaller fish meaning the only culprits to eat the fry would be the 2 Mollies, would they be capable of eating all but 2? And, secondly could she be pregnant and showing again so soon?
Crossbreeding between mollies and guppies is rare so it's more likely that one or both of the mollies was already pregnant when purchased. The rest of the fry will have been eaten soon after birth and the larger ones you've seen have been lucky enough to escape and grow. Livebearers can retain sperm and use it for several repeated pregnancies over 6 months or so, so it's quite possible for one to be pregnant again.