How to tell if the female guppy is pregnant?
It is easy to tell if the female guppy is pregnant – signs of pregnancy are a large belly, a boxy-look from the front view, and a darker gravid spot. The obvious black “gravid” spot is where the fry’s eyes forming inside the mother, and this is just in front of her anal fin.
When delivery is near, the female will start having difficulties swimming due the weight of the developing fry. The female will also try to find a hiding place, and will probably start refusing to eat. If you watch them daily during feeding times, you should be able to notice that they may not be eating. Even though some females may appear to ingest food, if you watch carefully they may often spit it out again.
Below shows a 2.5 weeks pregnant female guppy;
Rear view of the gravid spot;