How large can livebearers get before they can eat newborns?

[Scapexghost]

I have a 5.5 gallon tank that I use as a nursery tank. I have multiple tanks with all 4 of the common livebearer species so I'm usually adding adding a few dozen fry every week. So, this tank has various livebearers of various ages and sizes. So, my question is at what size will the fish be able to start gobbling up newborns and I need to move the to thw display tanks? I get that fish will eat anything that'll fit in their mouth, but it's hard to tell if a fry will fit in its mouth if they're not right next yo eachother. At that point, it's already to late. Assuming mouth size correlates to fish length, at what length are the fish's mouths big enough to fit a newborn fry into?

[Guppysnail]

At a juvenile age mine do not.  I have put the newborn fry in with 1 inch girls. Sometimes 1 1/2 inc. Even my whale girl adults are not voracious fry eaters though. I have to restrict food to keep numbers down when one gives birth. 
 

I have heard some folks note that some guppies are more prone to fry eating than others. I have had 3 girls that will obsessively chase fry even though they are well fed. The rest hardly pay any attention to them. 

[Scapexghost]

On 7/19/2022 at 6:21 AM, Guppysnail said:

At a juvenile age mine do not.  I have put the newborn fry in with 1 inch girls. Sometimes 1 1/2 inc. Even my whale girl adults are not voracious fry eaters though. I have to restrict food to keep numbers down when one gives birth. 
 

I have heard some folks note that some guppies are more prone to fry eating than others. I have had 3 girls that will obsessively chase fry even though they are well fed. The rest hardly pay any attention to them. 

Also guppies and mollies seem like less foracious fry eaters than platies and swordtails. I saw one female platy swimming in circles eating her own fry as they came out of her.

[Guppysnail]

On 7/19/2022 at 8:43 AM, Scapexghost said:

saw one female platy swimming in circles eating her own fry as they came out of her.

😳 oh my. Can I send my guppies over for training? 🤣

[Beardedbillygoat1975]

I would say that Xiphophorus are more aggressive in terms of pursuing fry particularly swords, platies less so in my experience I also keep dwarf platys at present so that is skewing my overall results (the variatus and milk/ink were good about fry as well). In terms of mollies and guppies - it depends on the line of them. @Bentley Pascoehas noted that the Blue Hawaiian Moscows do not seem to predate on their fry or certainly not enough for me to notice. However, I have had red dragons that did eat their fry. I have also had various mollies that have and have not eaten their fry. Black mollies I have never seen them eat their fry but my Lyretails did eat their fry. This is why there is so many answers when you put this out there is that it's part of their DNA. 

[JettsPapa]

On 7/19/2022 at 7:21 AM, Guppysnail said:

I have heard some folks note that some guppies are more prone to fry eating than others. I have had 3 girls that will obsessively chase fry even though they are well fed. The rest hardly pay any attention to them. 

That is absolutely true.  I've only been keeping guppies for about two years, but I can already tell that albino koi guppies are just about impossible to raise in a tank with adults, dumbo mosaics don't seem to bother fry at all, and golds are somewhere in the middle.