After a male guppy uses its anal fin to pass sperm and fertilize the eggs inside the female body, the female is expected to be pregnant. However, a female guppy can hold fertile sperm inside her for about ten months and use them to get pregnant afterward.
To tell if a guppy is pregnant, observe the area behind its anal fin where the gravid spot is located. A female guppy is pregnant if that area is darker than usual or has a dark shadow-like color/spot over it. The female also gets bigger with less activity or movement around the tank.
A female guppy can get pregnant as early as two months after birth, although they usually mature at three months. It might be difficult to spot a pregnant guppy immediately after getting pregnant, but the signs will appear within the first week.

How to Tell If a Female Guppy is Pregnant
The reproduction rate of guppies is very high because a female guppy can get pregnant even a few hours after giving birth. Their gestation period is between 21- 30 days. During pregnancy, the gravid spot gets darker and bigger as time goes by. When due for delivery, the stomach will also bulge.
Below are some of the signs to look out for:
1. Buldged belly
A pregnant guppy’s stomach will get bigger when she is pregnant. In the first weeks, the stomach will look bloated, but as the guppy approaches deliver, her stomach will appear large with a square appearance.
However, a big belly does not necessarily mean the guppy is pregnant. Guppy dropsy, bloating, constipation, or swim bladder illness can also cause a swollen belly. Examining the fish to overrule any of the above diseases is essential.
2. The gravid spot
Female guppies have a gravid spot near/behind the anal fin. The gravid spot may appear orange or dark but will get darker and bigger as the pregnancy progresses. You will see little dots in the gravid spot when the guppy approaches its due date. The little dots are the fry’s eyes.
3. Aggression
A change in behavior in pregnant females is very common and normal. Pregnant guppies fight off the male if they feel threatened. The fish will become aggressive and nip other guppies, especially when male guppies try to mate with her. Although this might indicate a guppy is pregnant, you should use other signs to ensure she’s pregnant.
4. Change in behavior after mating
Mating is quick among guppies; you will be lucky to witness it. Therefore, if you have seen them mating with a change in behavior after some days, the female may be pregnant.
During mating, a male guppy will chase a female around. The male may also do some dancing showing his beautiful tail to entice the female into mating. The male will insert his anal fin into the female’s and release sperm.
5. Loss of appetite
A pregnant guppy may lose appetite, or the appetite might increase. When she lacks appetite, she will stay in one place and not move even when you drop food. When her appetite increases, she will even nip other fish to have all the food to herself.
Lack of appetite could also be caused by being sick, so you should examine her closely. A pregnant guppy may not give birth due to poor diet and nutrition. Therefore it is important to ensure that they are eating.
6. Breathing rapidly
A pregnant guppy may have difficulty breathing, and you will see her strain. Rapid breathing mostly happens when she is close to giving birth, especially if she carries many fries.
Pregnant Guppy Signs of Delivery
After a guppy gets pregnant, it will take her 21- 30 days to give birth. The delivery takes 2 – 6 hours but sometimes lasts up to 12 hours. Sometimes the guppy will drop some fries, rest for a few hours, and then drop the rest. Below are signs that the guppy is going into labor.
1. Contractions
A pregnant guppy will get body contractions when in labor. Her muscles will tighten and then become relaxed. The process might repeat itself until she gives birth.
2. The guppy will hide
A pregnant guppy is very aggressive, especially when about to deliver. However, it will often try to hide away from other guppies or move to places it can isolate. The guppy will hide on plants or swim to the top of the tank.
3. Shaking and shivering
Although not all pregnant guppies will shake or shiver during labor, most will, indicating the fries are about to come out.
When to Separate a Pregnant Guppy
A pregnant guppy should be separated from the other guppies, especially males. Male guppies will chase any female within the tank to mate with her, whether pregnant or not. The chasing will stress the pregnant guppy, which is bad for her pregnancy. The pregnant guppy will also retaliate by nipping.
The pregnant guppy will need space during labor, and when the fries are born, the other fish will eat them. To ensure this does not happen, move the pregnant guppy to a separate tank on her last week of pregnancy or when you notice the above signs of labor.
If possible, prepare two separate tanks, one for the fries and one for the mother to recuperate after giving birth. The fries are at risk of being eaten even by their mother, so separating them will save them. The separate tanks will ensure you feed them appropriately.
You can move the mother back to the community tank 24 – 48 hours after giving birth. If you do not have a separate tank, you can use a mesh to separate the tank.
Can I Put Two Guppies Together?
Yes, you can keep two pregnant guppies together. Pregnant guppies are separated from other guppies because other fish will stress them and eat their fries after birth.
Although you can keep two pregnant guppies together, you should have a strategy to protect the fries after birth because even their mother will eat them.
You can put many plants and decorations inside the tank for the fry to hide, but still, their survival will not be guaranteed since hungry mothers and even tank mates like kuhli loaches can eat guppy fry.
The best way is to separate the tank with a mesh and keep the fries on one side.
Recap
A pregnant guppy can get pregnant when she is two months old. The pregnant guppy belly will bulge, and the gravid spot will get bigger and darker. The pregnant guppy will also get aggressive, lose appetite, or eat a lot.
When she is in labor, the pregnant guppy will have body contractions; she will swim in place or try to hide. When the guppy is in labor, separating her from other guppies is important. Also, you should separate the mother from the fries after giving birth because she will eat them.