Question
I have two tanks with around 30-40 guppies and when I have re-arranged the substrate / plants / decorations I sometimes find that one or two baby guppies 'appear'. The mother does not look pregnant at all and these guppies seem less than a week old and this has happened twice now.
All of these guppies, except the mother, are ones which I have bred myself so I am well aware of what a pregnant guppy looks like and what the week old fry look like.
The mother guppy has given birth to around 10-20 fry each time and when these new 'fry' appear, they are considerably smaller than the 2-4 week old fry.
So it almost seems like when the guppy has given birth, a few fry have hidden and then when rearranging the tanks, these fry reappear but have not grown like their siblings. Is this a possible reason? Or is there another explanation?
Answer
Guppy`s can (and will) get pregnant at the age of about 7-9 weeks old this means they will give birth to their first babies in week 10-12.
Guppy babies will hide as soon as they are born and they can be very hard to see against the background gravel-plants-ornaments and other aquarium equipment.
Female guppys can store sperm for months and can be pregnant multiple times from one mating,Female guppys can select the sperm from one or more male after multiple matings so they can select and use the sperm from the male they see as most fit.
It can be hard to see if a young guppy is pregnant with few babies,like 3-5 fry.
Some of this answer is from my own experience,the rest is in this source https://en.wikipedia.org/wiki/Guppy
When a female guppy can get pregnant will depend on the breed,and if there is predators in your tank they tend to get pregnant at a younger age.
Answered By - trond hansen