A female guppy's pregnancy usually lasts four to six weeks. A female guppy that is getting ready to give birth usually appears fat and has a dark spot on her abdomen that grows larger as her pregnancy progresses.
Guppies are among the easiest fish to mate, and a guppy can produce several broods from a single mating. Observation is the best way of determining when a female guppy may be ready to give birth. When she appears close to delivery, she can be isolated in a breeding trap to protect her fry from hungry adult fish. The mother fish should also be removed after she has given birth.