I do have some aquariums in the house - this is an additional aquarium for surplus fish from breeding to store whilst I try and give them away.

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.

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?

@blacksmith37 ah the temperature has been quite high in the UK recently - I will add that into my question.