How Long Are Molly Fish Pregnant For? Twice As Long As Guppies!

Dec 17, 2021

How Long Are Molly Fish Pregnant For?

Mollies are livebearers. They give birth to healthy, free-swimming fry born ready to forage and explore. No eggs, no hassle! In fact, it wouldn’t be wrong to compare mollies with rabbits – no exaggerations there! So, how long are molly fish pregnant for? And how long does labor last? 

In this blog, I’ll be answering these questions alongside many more revolving around mollies, pregnancies, and babies! 

Hop in! 

How Long Are Molly Fish Pregnant For? 

Molly fish are pregnant for anywhere between 40-70 days, with 60 being the most common number. Their pregnancy duration is twice as long as a guppy’s, who remain pregnant for just 21-35 days. 

A molly’s gestation period is subjective to variables like the fish’s age, health, size, and experience level. Usually, mature and big fish give birth to greater numbers of fry than inexperienced and young females. 

Factors like the water parameters, diet, and stress levels also play a pivotal role in determining the gestation period. 

So, as you can tell by now, we’ll never know for sure then your pregnant molly is going to ‘pop’. But still, I’m pretty sure the answer would lie somewhere between 40-70 days! 

That being said, there are going to be a few anomalies. 

On forums, I came across some owners who shared that their prodigies gave birth within 20-30 days. Whereas other hobbyists reported that it was months before their fish showed any sign of labor. 

Now that the main query is answered, let’s look at some equally beguiling and informative questions and answers. 

Relevant: What Do Molly Fish Eggs Look Like? Little Yellow Balls!

Molly Fish Pregnancy Stages 

Credit: Dennis Amith (Creative Commons license)

The molly fish pregnancy stages can be divided into 5 parts:

  • Conception 
  • Formation of embryo 
  • Fry’s development 
  • Pre-birthing stage 
  • Birth

Conception 

If you have mollies of both sexes in your tank, know that fry will be there too anytime soon – there’s not much you need to do for them to mate. The male will pair up with multiple females during one mating season. He will court and coax the female until she gives her consent. 

The male will then deposit milt, a fluid that contains sperm, into the female’s opening using a gonopodium. 

Gonopodium refers to a unique anal fin that’s somewhat shaped like a rod instead of a normal fin. 

Formation Of Embryo 

All of the fertilized eggs will develop into embryos. The ones that weren’t fertilized will retain the yolk-like yellow color. 

If you have a keen eye, you can see the development of embryos happening inside your molly. Just look at the gravid spot. 

You can observe this behavior usually after 7-10 days of fertilization. 

Fry’s Development 

As the young fry continue to grow inside the molly fish, the mother’s body will become unmistakably swollen and distended. 

Each embryo is fully equipped with nutritive elements the mother’s body initially provided them with. They feed on it during their development. 

Pre-birthing Stage

The matriarch prepares her mind and body to give birth at this stage. You can even see the fry’s eyes visible through the thin areas of the gravid spot. 

Fully developed, the fry will lie in a semicircular position and get ready to venture out. 

Birth 

Once the labor begins, the birthing process can take anywhere between an hour to a full day. Once again, this is a wide range for an answer, I know, but it depends on many different factors like age, health, and environment. 

The fry are delivered one at a time – usually, the tail comes out first. Upon birth, the fry fall a few inches through the water. 

But born ready, they will quickly straighten out and swim for cover. 

If there’s no cover nearby, the fry will swim to the bottom and take refuge in the sand and rocks. They will often lie motionless for some time as they gather strength. 

Unfortunately, mollies are known to eat their own offspring. 

Therefore, you can place the expecting molly into a separate tank or a breeding box. And once she’s birthed all the fry, quickly move her to the main tank. 

A 10-gallon tank with a bare bottom, sponge filter, and proper aeration would be ideal for the fry. 

However, managing a separate tank may not always be practical for us all the time. 

So, you can use a breeding box like this one from Fluval! I use it for my mbuna cichlid tank, and it works pretty well. 

A few hours after birth, molly fry can eat pulverized flake food, baby brine shrimp, and daphnia. 

Five Signs Of A Pregnant Molly Fish 

The most evident sign of pregnancy in mollies is the belly area’s distended, rounded, and swollen appearance. They will also appear more aloof and intolerant. In most cases, the appetite will increase quite a lot, but they can also stop eating if they aren’t feeling right. The appearance of the gravid spot is another tell-tale sign of pregnancy. 

Swollen And Distended Belly 

No-brainer here! The most obvious sign of a pregnant molly fish is a swollen and distended appearance. She will look more chubby – especially around the belly area. 

That’s because the mother’s body will expand quite profusely to accommodate the fry. 

Although the eggs and fry are incredibly tiny, that many of them will force the female’s body to get a lot more rounded than usual. 

Change In Behavior 

Mollies are peaceful and friendly for the most part. But when a female is expecting, she will become more anxious, intolerant, and possessive. 

Although she’ll rarely attack anyone, she will make her discontent known to anyone who disturbs her. 

She will also keep to herself more often and try to hide around. 

Therefore, you should house as many plants and hiding places as possible. 

The change in behavior can be noticed as early as just 7 days after conception. 

Change In Appetite 

Pregnant mollies will usually eat a lot more than usual as their bodies need more energy to compensate for all the developments happening inside.

However, in some cases, the expecting molly will stop eating. She will lose her appetite. And this isn’t normal. The fish could potentially be under stress for some reason. 

Prominent Gravid Spot 

The most surefire way of telling if your molly is pregnant or just getting fat is checking the gravid spot – a dark, triangular mark that’s positioned towards the anal cavity. 

As the pregnancy proceeds, the gravid spot becomes darker and larger. Upon close inspection, you can even see the fry’s eyes through the light parts of the spot. 

However, it’s hard to spot the gravid spot – let alone eyes – in black mollies.

Chasing Heat 

Pregnant mollies need to remain at a constant temperature throughout the gestation period. Therefore, you will often find them hovering near the aquarium’s heating system or temperature stabilizer. 

If your tank uses an overhead UV light, you will see the mollies hovering closer to the surface. 

How To Know Molly Fish Is About To Give Birth?

Credits: Dennis Amith (Creative Commons license)

It’s critical to know when the molly fish is about to give birth so you can transfer her to a different tank. Usually, the gravid spot grows more prominent than ever, and there will be a bulge below the gills. The fish will try to hide often and stop eating. If you have sharp eyes, you can even see the fry’s eyes inside the mother!

The Gravid Spot Becomes Prominent 

The gravid spot grows super prominent and dark when your molly fish prepares to give birth. You can easily notice it. However, it may be harder to observe in black and darker colored mollies. 

Molly Grows A Bulge Below The Gills 

Your molly will develop a strong bulge below the gills a few days before the delivery. This will result in a fairly square outline around this region. 

This indicates that the ‘womb’ has reached full capacity. The fish will now want to give birth as soon as possible to alleviate any strain. 

Hiding Behavior Increases 

A heavily pregnant molly will look for a quiet and secluded area to give birth in peace. She will try to take refuge under plants, inside caves, and behind rocks. 

They’d greatly benefit from any strategically placed hiding area in the tank. 

You Can See The Fry’s Eyes 

As the embryos reach the final stages of development, you can see the eyes through the light areas of the gravid spot. Once the eyes become perfectly visible, it won’t be long before the mother gives birth. 

Molly Stops Eating

During pregnancy, mollies often have a voracious appetite. However, when labor is imminent, the fish will stop eating. She will not swim to the surface even when you’re offering food.

Frequently Asked Questions 

How Often Do Mollies Have Babies? 

Mollies can have babies once every 30-45 days. As a matter of fact, once sexually mature, they can have babies throughout the year. 

Can Molly Fish Get Pregnant Without A Male?

Mollies are known to store sperm inside their bodies for several months after mating. They can then use the deposited sperm to fertilize eggs and produce babies. 

So, in a sense, yes, mollies can get pregnant without a male around. 

Some hobbyists have reported that their mollies gave birth 6 months post-mating. 

Therefore, we cannot rule out the chance of pregnancy even in an all-female tank. The molly you just bought may already have sperm stored safely inside her body. 

How Many Babies Do Mollies Have? 

On average, a molly fish has anywhere between 40-100 babies during one window. It’s been reported that the number can go up to 120. 

Once again, the number of fry is dependent on parameters like how old the fish is, its health status, and how conducive the environment is. 

The record for the highest number of babies delivered by a molly in a year is 570! But note that it was through multiple births. 

How Big Are Molly Fry?

Generally, molly fry are about ¼” long. By the time they’re born, they will have fully formed fins. They will pretty much look like miniature versions of adult mollies. 

Do Mollies Eat Their Babies? 

Yes, mollies most definitely eat their babies. And unfortunately, the concrete reason behind this is still unknown. 

Researches point out that filial cannibalism is a spill-over response triggered by stress, enhancing the fish’s self-preservation instinct. 

Another plausible explanation is that mollies do so to weed out the weaklings. 

When Do Molly Fish Sexually Mature? 

Mollies sexually mature at around 4-5 months of age. Therefore, if you are not enthusiastic about having tiny molly fry, you need to separate the males from females before they are sexually mature. 

Where’s The Gravid Spot On Molly?

The gravid spot is situated right behind the anal fin in livebearers like mollies. It’s a darkly colored spot of the womb that grows larger and darker as the pregnancy advances. 

The gravid spot is the most commonly used indicator of pregnancy in livebearers. 

What’s Pregnant Molly Fish Behavior Typically Like?

A pregnant molly fish will become more aloof, irritable, and aggressive. She will be intolerant of anyone meddling with her or encroaching her space. 

Initially, the appetite will increase. However, she will stop eating towards the end of the gestation period. 

Final Words: How Long Are Molly Fish Pregnant For? 

Molly fish are pregnant for around 40-70 days. The fish’s age, health, size, and experience level play a determining role in their gestation period. 

Mollies are livebearers. They give birth to free-swimming fry that are about ¼” inch long. And during one mating season, they can give birth to around 40-100 babies! 

Since mothers eat their own babies, it’s best to raise fry in a separate tank or a breeding box. 

rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.