Female guppies can easily become pregnant when they're in contact with male guppies. If you keep your guppies in a mixed gender tank there is a good change one or more of your female guppies are pregnant. Once you verify a guppy's pregnancy, make sure to put it in a separate fish tank. To ensure the safety of the baby guppy, known as a fry, keep the fry in a separate tank until it reaches maturity.
Like most animals, the bellies of pregnant guppies grow larger during pregnancy. A pregnant guppy's belly looks much like a cube. This is especially true when you look directly at the guppy, as if making eye contact.
The gravid spot is a light-coloured spot near a female guppy's tail. When a guppy becomes pregnant, its gravid spot darkens. Sometimes, near the end of pregnancy, you can see small, darker splotches on the gravid spot. These spots are the eyes of the female guppy's unborn fry.
A female guppy will typically rest during the last few days before delivery. It may refuse to swim completely or simply swim more slowly or more infrequently than usual. If your guppy is particularly lethargic, it may be ready to deliver the fry.
When a guppy is ready to give birth, it refuses to eat. This generally only affects a guppy during the last 12 to 24 hours before birth and signals a guppy that is very far along in its pregnancy.