Mature females are full bodied and have a gravid spot which is a dark spot near their vent. Males are much more colorful. They also have a gonopodium which is a modified fin which delivers sperm into the female. Breeding Keep a few females with a male. He will impregnate the females.
Guppies are usually able to first breed by the age of three months.
One mating can fertilize several batches of live-born fry. After breeding, the babies develop over one to two months depending on water temperature and the health of the mother. She can give birth early or delay birth depending on her health and stress level. It is common for newly bought female guppies to give birth months after being obtained even when kept in a tank devoid of males. Females have a gravid spot which is a dark spot near their vent.