How do I know when my guppy has finished giving birth?

After a guppy finishes giving birth, her abdomen usually shrinks from its swollen round shape and returns to its original translucent color, with the dark gravid spot gone. Also, a guppy that has finished giving birth will pass a relatively thick stool. If the owner didn’t observe this, they can drop a small amount of food into the tank — guppies generally don’t eat while giving birth, so if she starts eating, she’s done. Each birthing session usually lasts no more than a day; a first-time mother produces about 10 fry, the second around 20–30, and the third possibly 30–50.