How to Identify a Pregnant Guppy (What to Look For)

If you own a few Guppies then you know you should always be expecting babies. Guppies are some of the most prolific fish on the planet. Even in poor conditions they will regularly live young.

But what if you want to plan a bit to try and save some of the babies from their always-hungry parents? To do so, you’ll need to know when your female(s) is carrying. So how does one tell if a Guppy is pregnant?

How to Tell if Your Guppy is Pregnant

While it’s always easy to tell if a heavy carrying female is pregnant sometimes females may only have 10-20 babies or less. Since female Guppies tend to be always a little chunky how do we tell if your Guppy is pregnant?

The best way to tell if you guppy is pregnant is to watch for changes to the female’s gravid spot. In pregnant guppies, the gravid spot often grows larger and darker and the babies grow.

What is the Gravid Spot?

The gravid spot is actually visible most of the time in most female Guppies. It’s the darkened skin of the womb where the fry develop after the eggs are fertilized. Guppies, unlike most fish, are live-bearing.

gravid guppy

They do create eggs however they are fertilized internally by the male rather than laid externally. The male Guppy has a penis-like organ called the gonopodium that’s actually a modified anal fin. He inserts this directly into the female’s reproductive tract to inseminate her.

Once the female has developed young inside of her, her belly will begin to swell and the gravid spot will darken. The mother Guppy is so small that her skin is translucent, allowing you to partially see within.

In the last few days before birth you may even see the eyes of the young Guppies through the gravid spot! This often happens if she’s carrying heavily or is an especially large female.

As the gravid spot changes so does her behavior. The pregnant female may begin to shun food as birth approaches. She may isolate herself, spending more time in the corners of the tank or hidden among plants. This is to provide as much protection for her fry as possible once they are born.

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These changes start at around three weeks after being impregnated by her mate. Once you start to see the gravid spot darken and her behavior change, it’s best to move her to either a separate aquarium or a breeder box.

Breeder boxes are the gold standard for live-bearer birthing spaces. They have water circulation so the adult Guppy can breathe normally. Yet they isolate the babies from not only the other fish but their ravenous mother.

After giving birth the female quickly forgets who her babies are and will likely gobble them right up if she comes across them again. A breeder box hangs on the side of the tank, creating an easy nursery for the young fry to develop in!

How Many Babies Will My Guppy Have?

The number of babies Guppies have varies wildly. It depends on the genetics of the parents, food availability, and both the size and maturity of the mother. New moms tend to be smaller and have fewer fry on average. As they grow and have additional pregnancies the number of fry per birth tends to increase.

Female Guppies can become pregnant once a month on average. This is close to the same as other Livebearers like their cousins the Platy, Swordtail, and Molly. Guppies however are called “Million Fish” for a reason. They often have back to back pregnancies with little rest period once they find a home to their liking!

The female’s gestation period is actually around 24-35 days. It depends mostly on the water temperature, her health, and how much food is available. If conditions are poor, gestation may be delayed or even terminated.

Once the female is pregnant the gravid spot mentioned earlier is what you need to watch out for.

pregnant guppy giving birth

Guppies Can Store Sperm

Believe it or not you can end up with a pregnant female Guppy even if you don’t think there are any males around to fertilize her! Guppies have the unique ability to store sperm within to use later for pregnancy.

While science has mostly known of this, it took the efforts of researchers at the University of California: Riverside to find the exact length of time. As it turns out, female Guppies can store sperm for up to 10 months before using it to fertilize her eggs internally!

This ability was probably evolved in order to delay going through the stressful, dangerous period of pregnancy if conditions are poor. Female Guppies are larger and better swimmers than males as well. They can therefore find new habitats and have more body mass to weather starvation episodes.

Even if their numbers crash and there are no males around the stored sperm within the females will allow them to quickly repopulate a body of water with baby Guppies. So even if you own only a single female Guppy, if she was ever around males in the pet store you may end up with fry in the late future!

Preparing for Baby Guppies

If you don’t want to set up a separate tank or breeder box for your Guppy fry you do have a few options to think over. In an aquarium that’s large enough and has enough cover, a few Guppy fry are always guaranteed to make it to maturity. Most will be eaten by the other fish but not all if there’s enough places to hide.

Thickly tangled live plants offer the best cover for young Guppies. When live plants get brought up, many aquarists think about complex full spectrum lighting and expensive additions. However there are a number of plants that provide adequate cover with little fuss.

Three of my favorites are Java Moss (Vesicularia dubyana), Hornwort (Ceratophyllum demersum) and the perfectly named Guppy Grass (Najas guadalupensis). All three of these plants are famous for their ability to thrive even in low light aquariums.

They are also fantastically versatile in how you grow them. In fact, you could easily aquascape an aquarium with just these plants, a basic light, and some standard gravel.

Hornwort and Guppy Grass will grow both rooted and floating. Java Moss will grow either floating or attached to hard surfaces, like rocks and driftwood.

Between the three of these plants you can have a gorgeous tank that provides loads of cover and feeding places for your baby Guppies. Live plants also tend to cultivate infusoria (single celled organisms) and other tiny things that your newborn fry enjoy eating.

Caring for Guppy Fry in a Separate Tank

Once your Guppy fry are safe in their new home, be it a breeder box or separate aquarium, feeding them is going to be your first priority. Livebearing fish have live young because it offers a survival advantage over egg laying fish.

Livebearer fry are very large and well developed. They can swim freely much sooner than most egg layers and quickly begin foraging for food. This fast development allows them to become sexually mature and breeding in as little as 2-3 months!

Even newborn Guppies can handle relatively large food items. Since you’re already very well prepared for them you should have plenty of live brine shrimp nauplii on hand to offer them.

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Brine shrimp nauplii are some of the best possible foods for baby fish. Rich in both fat and protein, they also wiggle enticingly and are perfectly sized. If you aren’t a fan of raising your own nauplii you can try offering them dead but prepared in a liquid solution. 

These are much more convenient to keep in storage. Also the scent alone may be enough to trigger a response but the movements of live nauplii are hard to beat.

Conclusion

Breeding Guppies is richly rewarding and an experience both novice and expert aquarists can enjoy. The female doesn’t do a very good job of caring for them so you’ll have to step in. And by recognizing the signs, you’ll be able to tell and prepare for your Guppies’ pregnancy with ease.

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