Is My Molly Fish Pregnant Or Fat? How To Decide?

Molly fish are prevalent fish among aquarists to keep due to their vibrant colors, excellent body structure, and easy-going nature. The most important part of getting them is the ease of breeding which makes them irresistible for many fish breeders. But, sometimes, there is confusion that lingers in the back of the head when we start to see changes in the size of molly fish. How to clear this confusion lingers more than it should? What if molly fish is just fat, not pregnant, and you end up waiting for fry that was never there?

I know both fat and pregnant Molly fish shows similar signs. However, there are various signs such as the change in appetite, squared or plumper body, and visible black lines that can help differentiate between Molly fish obesity or pregnancy.

Your molly fish gets fat all around the body, not just in the lower region. Mind you; they are towards the square side of growth than rounder during pregnancy with visible darkened lines proving the presence of fry in their belly.

In this post, we will be discussing Molly’s fish fat or pregnancy in detail. So, please keep reading to know more about Molly fish and their pregnancy signs.

Reproduction In Molly Fish

Molly fish can reproduce quite often, especially in a community tank. Therefore, they will usually choose to have babies during the springtime and other times throughout the year.

For these fish to breed, you need at least one male and female Molly together in the same aquarium that is large enough to live comfortably.

Do not keep two male mollies in the same tank without keeping the female mollies enough to maintain the ideal ratio.

These fish are livebearers which means that instead of the female Molly laying eggs, molly fish gives live birth to baby Mollies.

After around 20-60 days of gestation period of molly fish, the fish will produce approximately 40- 100 molly fry. The males will protect and guard these fish until the fry are big enough to be on their own.

What Are The Signs Of Pregnancy In Molly Fish?

When Molly fish are pregnant, they will become fat. It is because of the fry that she is carrying inside of her. But the signs of pregnancy in Molly fish are:

Huge Appetite

Molly fish will eat more than usual when they are pregnant. Okay yeah, these fish will overeat when they are on the obese side of the weight scale.

Pregnant Molly fish will eat too much for most of the gestation period. But they will stop eating when they are going to give birth. This is your ultimate sign that they are pregnant and far from obesity.

Although it means that you will see an abrupt change in their appetite and activity levels, don’t try to feed Molly fish once they have stopped eating because it will be useless.

Visible Black Lines

You will start to notice black dots or lines after a few days of them looking plumper. Now, let me point you in the direction where you will find the black lines or dots.

Look at the anal vent near the anal fins of the molly fish. You will see some black dots and lines if your fish is pregnant. Let me explain, those black dots or lines are the fry developing inside female molly.

Honestly, this is the very sign that will confirm the pregnancy and throw the confusion about obesity out of the window.

Hiding And Secluding

They become very protective of themselves as these female mollies get sensitive and vulnerable while carrying the fry.

You need to understand her for wanting solitude during her most vulnerable state. Can you imagine these molly bumping into every fish in the tank?

Mollies tend to hide more often when the tank is overcrowded or there are fish that are bound to irritate them.

I suggest you separate the pregnant mollies and keep them in a breeding tank throughout the molly fish breeding cycle.

Change In Color

Have you ever heard of a change in color or turning pale when someone is sick or weak? Well, can you expect your fish to act any different when they are weak?

It is understandable for molly fish to lose a little brightness or become a little paler when they are pregnant.

Don’t worry, they will get their color back once you start feeding them good and healthy food. These mollies will change color and become their vibrant selves post-delivery as well.

Sudden Aggression

During this time, the female Molly may act aggressively towards other fish near them or try to nudge their belly, which can be dangerous when pregnant.

In addition, Molly may nip or even eat other small fish if they are too close to her belly, which has the fry inside of it.

Do Molly Fish Show Similar Sign In Pregnancy And Obesity?

Molly fish may look like they are pregnant due to their large abdomen. With certain parasites or infections, Molly fish can also develop a rounder and enormous belly, but it is often more triangular.

If your fish has been eating well and seems active, there might not be too much cause for concern. Mollies are often very round and bloated, looking after a big meal of pellets or brine shrimp.

Remember, pregnant mollies are more on the square side than triangular and rounder ones. Also, the black lines and presence of fry in the belly will hint you in the right direction.

If you see no other signs than weight gain in molly fish, you might have to call your vet for suggestions. This will generally go down over time without any intervention necessary on your part. 

Signs That Show Molly Fish Are Fat, Not Pregnant

I know it is easier to distinguish pregnancy from obesity when you understand where you need to look. So I am not surprised if you have skipped the whole paragraphic sections to jump into the numerical list, so I will give you that.

Who wants to read the bulks when you can simply see the

Some of the signs that Molly fish are fat but not pregnant are:

  • Molly fish are swimming vertically or upside down due to bloating or too much fat in the body.
  • They are with a bloated abdomen or swollen belly that is rounder than usual.
  • They have a yellowish coloration
  • Mollies will find difficulty in breathing
  • They may have red streaks or spots on their white underbelly
  • Molly fish will eat too often and produce more waste.

How To Prevent Molly Fish From Becoming Fat?

Molly fish are omnivorous. They will eat everything you give them, from plants to smaller fish. So, owners are more likely to overfeed Molly fish. However, some of the tips to prevent Molly fish from becoming fat are:

Feed The Right Amount Of Food

You cannot and should not overfeed any aquarium fish. Trust me, nothing good comes out of overfeeding and obesity and you may even lose your pet during all the chaos.

Make sure to feed these mollies only what they can finish within 2 to 3 minutes or the amount that equals the size of their eyeball.

It is not that hard to keep an eye on the quantity, however, quality is also equally important in this scenario. Never forget that.

It would help if you fed Molly fish enough pellets, flakes, wafers, live food like bloodworms, daphnia, etc., or veggies such as cucumber, zucchini, etc. 

Do Not Give Too Many Vegetables

I know this is an easy resort for you to prepare and feed molly fish vegetables present in your refrigerator. But it is not ideal to feed them way too many vegetables without even considering a meaty diet.

I hate to break it to you but trust me, your molly fish might have easy bowel movements but a weaker immune system.

Make sure to alternate the type of food for molly fish and balance between veggies, a meaty diet, and commercial food should not overdrive your wallet.

Maintain A Healthy Environment In The Tank

Molly fish need a healthy environment to live and survive. You cannot drop them in the tank and expect them to act all giddy and happy.

Molly fish require more oxygen, so you can use an air pump or filter for Molly’s fish tank to provide lots of oxygen in the water.

Stressed fish are more likely to eat more and become fat. Molly fish also need good lighting, so ensure that you use the right amount of tank lights to keep them active.

How To Take Care Of Fat Or Pregnant Molly Fish?

Molly fish needs special care when they are pregnant. This is because fertilization of Molly fish eggs occurs externally.

They give birth on the leaves of plants or other surfaces in your aquariums. The male Molly will swim alongside the female and brush against her belly to stimulate delivery, referred to as “Tail-Biting.”

Besides this, fat Molly fish also needs proper care. So, some of the ways to ensure the safety and care of pregnant Molly fish are:

Separate Fat Or Pregnant Molly Fish

It is better to keep Molly fish separate during the breeding period. Once Molly fish are pregnant, it is important to give them enough space to give birth without any problems or stress.

Fat Molly fish are more likely to compete for food and show aggression. These fish also needs a special diet to manage their weight. Thus, it is best to keep them separate.

Sometimes Molly female might eat their fry due to a lack of nutrients and proper care. So if you are keeping all Mollies together, it is advisable to separate fat and pregnant Molly fish.

Your fat molly will eat the food that is meant for their tank mates which you no longer want them to eat. While the pregnant mollies will get tortured by various tank mates making them lose their pregnancy.

Feed Molly Fish Properly

Molly needs their diet adjusted with more protein and calcium during the breeding period. So feed Molly some live food like brine shrimp or bloodworms. Feed them twice a day for better results on the reproduction of Molly’s species in an aquarium.

Monitor Molly Fish For The First Week

After Molly fish gives birth, monitor them for the first week by providing optimal conditions like clean water and a proper diet.

Also, make sure that Molly’s pregnant fish are safe from other aggressive creatures in your aquarium. It is also important to separate Molly females after they are pregnant so their fry can hatch in peace.

Molly fish needs a few days to recover from the delivery process, so make sure they have enough time before you put them back in your aquariums with other Molly species.

Introduce Fat Or Pregnant Molly Fish To The Group Slowly

After separating the fat or pregnant Molly fish and giving proper care during their resting period, you must introduce Molly slowly to Molly’s group by adding a small amount of water from the tank into the new aquarium.

It will allow their group members, like male or other pregnant females, to recognize each other and reduce their aggression towards female molly that has given birth recently.

Monitor The Water Quality Of Your Aquariums

Maintain your Molly fish aquariums by checking the water quality regularly and doing partial water changes at least once a week. Also, make sure that Molly’s tank has enough space for these fishes to swim around and stay healthy.

Make sure you are giving pregnant fish proper care by providing a nutritious diet, a clean environment, and optimal living conditions during their breeding period.

Molly females need separate space to give birth and recover after that. You should monitor the tank for the first week for the molly fry to stay healthy and happy in the tank. 

Maintain Healthy Environment

Maintaining a healthy environment is very important for Molly fish when pregnant. Ensure the breeding tank has clean water with low ammonia and nitrite levels, a pH between seven to eight, and a proper temperature. Molly fish need 70-80 degrees Fahrenheit during the pregnancy period in an aquarium.

Also, Molly fish might need a little salt in the breeding tank due to the origin of mollies, and mimicking their natural habitat will fuel the breeding behavior.

These fish can produce many fry quickly, and female mollies might die after having the fry due to the huge pressure and toil pregnancy brings.

So take good care of Mollies when pregnant to give birth to healthy fry for development later on. But you need to take care of molly fish fry while taking care of molly fish that just gave birth.

Some FAQs

How Long Will Molly Fish Become Pregnant?

Once you introduce Molly fish into the tank, they have a gestation period of approximately 60 days. But some Mollies even give birth to their young ones as early as 20 days.

Is Molly Fish More Likely To Get Fat Or Pregnant?

Molly fish eats almost everything, even the dead fish they see in the tank. Besides this, these mollies are omnivorous and eat both plants and animals.

So, they are more prone to obesity than pregnant, given that they are still in the first section of the growth stages in molly fish.

Moreover, when Molly fish lives in an environment with a male population and appropriate water condition, they are more likely to get pregnant more than twice a year.

How Many Babies Does Molly Fish Have?

Molly fish typically has around 80-120 babies after being pregnant for 20-40 days. The gestational period of Molly fish is about 60 days.

They are constantly pregnant if they live in a suitable environment with enough male population. You need to feed good food to baby molly to make sure they can survive in the tank.


In conclusion, Molly fish can either get pregnant or become obese if you miss a few moments here and there. But in either case, you need to buckle up and start taking extra care of your mollies in the tank. I know how risky it can get when the pregnancy or obesity reaches aquarium fish. But, trust me, your molly can die easily when you don’t ensure the diet and tank condition when they are fat or pregnant. So, you must be very careful in the diet and environment of your fish after you notice some unusual signs in them.

Hopefully, this blog post will answer all your questions about the obesity and pregnancy of Molly fish. Thank you for reading! For more information, don’t hesitate to get in touch with us.

Good Luck!!

Happy Fishkeeping!!

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