Is there some sort of resource showing the stages of a platy's pregnancy? I'm 100% sure my platy is pregnant, but would like to see a size comparison as to how far along she is. I don't want to mess this up! Thanks!

BTW she is a very dark blue tux platy so a gravid spot would be impossible to notice.

Hi, I'm not so sure that their are actual stages of pregnancy for platys. A lot of info is estimated by changes in female size, eating habits and gravid spot (depending on color). Platys can have a batch of fry every 18 days. I have 4 platys and a male swordtail and my platy is on her second batch of fry. They are smaller than a pin when born and almost colorless. It is common for females to eat their babies right after birth. Either isolate the female in a breeder before delivery or make sure your tank is well planted for babies to hide.

The female has the eggs inside, but is simply holding them. What happens to her body depends a lot on how many eggs are fertilized in there. In fish like Goodeid livebearers, where there is a connection between the developing young and the mother (or in mammals like us), there are stages in pregnancy, but a platy isn't really pregnant. She's carrying eggs internally.

It makes timing the drops harder, as a fish with very few fertilized eggs won't look that heavy, while one with a lot can look ready to pop for two weeks. I go by changes in the colour of the gravid spot (that won't help with your fish) and in shape - early, the area around the chest is angled, closer to the drop, the eggs seem to move forward and the body squares.

With experience, you'll see patterns, but it's hard to be precise.

I have learned they are only really cannibalistic in small tanks, and in a planted tank where the babies aren't constantly passing before their mouths, very few young get eaten.

A Platy doesn't just carry eggs, but eventually young. So at some point they are pregnant. Not the case for most fish I know. How many days have the young hatched before she releases them?

Ahh, so it's really dependent on the individual fish. Well, if they drop eggs every 18 days then I shouldn't be too bothered if I miss the first batch. Will just have to keep observing! Thanks for the very informative replies!

A Platy doesn't drop eggs. They hold eggs until they hatch inside and then they release the young. If you see a Platy dropping eggs that would be them aborting.

Gary your knowledge on livebearers is amazing!

Ive no real info to add to this thread,sorry,but good luck and i hope ya get lots of fry!Would love to see pics of the mother fish she sounds beautiful!

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I started trying to find proof for Jrman's point, because it is a good one. From a couple of papers I found online it seems the egg hatches internally and the fry is expelled straight away. I don't think the fry lives inside the mother except to move on out. It does however live inside its perfectly transparent egg, like its close relatives the killifish. That's why when a very gravid female's skin is stretched, you can sometimes see the eyes of the young peering out at you through the transparent skin and egg shell.
I've been able to use a school digital microscope to film red corpuscles moving through the heart of a killifish embryo, the eggs are so clear.
What absolutely blew me away in my reading was a study on the weight of their eggs. They are the same weight at fertilization as at hatching, although I assume they expand in size as the embryo and then fry develops. But it takes energy to grow - straight up egg layer eggs lose up to 30% of their weight as they grow. These fish do nourish their young in the womb, maybe through follicles found there. They seem to provide enough energy to maintain the weight through development, something I did not understand before. That is cool. Apparently, they may be able to transfer carbs to the developing egg.
Nerds like me love learning new stuff like that.
Goodeids, a different evolutionary line of mostly Mexican livebearers have actual umbilical cord structures (two per fry) and breeders have to be careful with that. They evolved in scarcity with a high plant diet - lots of fibre which they make the most of. If we feed them high protein fish food while they are gravid, the babies outgrow the birth canal and both mother and baby die.
With swords, platies, mollies and other Poeciliid fishes, there is a poorly understood shut off mechanism. The fry apparently never weighs more than the original egg.
And here I was, just before I read that message, thinking the eggs sat in Mom unaffected by her, til they hatched and the babies dropped out. You live and learn.

Well, the mom died unexpectedly. I was going to get a picture of her before I turned the lights out for the night, and I found her in the all too familiar nose-in-the-gravel pose. Is it common for livebearers to die while carrying? She was showing no signs of illness, nor have my other fish.