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?

  • Do you have only one female? Because you speak aboit one mother only... Aug 23 '21 at 9:45
  • There are other females which are 3-4 months old, the first offspring I had from the mother, however these have not appeared to be pregnant. The other reason I think this might not be the case is that this seems to happen immediately after rearranging the tanks - unless this triggers something within the guppies to cause them to give birth?
    – Jsk
    Aug 23 '21 at 10:11
  • 1
    i have a hard time figuring out what you are asking here,guppys are always pregnant and guppy fry do hide it is how they survive to be adults.when you disturb their hiding places you see them,if you did see them all the time then they did not hide very well and are unlikely to survive.and pregnant guppys can delay giving birth until it is safe for them to do so. Aug 23 '21 at 10:52
  • The question I have is having multiple guppies, which I suspect are siblings, at very different sizes - some appear to be a few weeks old and some appear to be days old and these only tend to appear when I have rearranged a tank.
    – Jsk
    Aug 23 '21 at 11:14

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.

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