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How To Tell If Your Glofish Tetra Is Pregnant?

Glofish might be man-made genetically engineered fish but boy it is pretty isn’t it? And if you are wondering about the baby glofish, then let me tell you how beautiful they look while growing. Although there is an illegal word attached to breeding glofish, how can someone win over nature? If you have male and female glofish tetra in the tank, you can’t change the inevitable. Female tetra is bound to get pregnant when they hit sexual maturity and is in the presence of male glofish tetra. But how to tell if your glofish tetra is pregnant?

Curved belly to swollen bellies is what gives the pregnancy in Glofish tetra away. Although it is hard to tell males and females apart, it will be quite evident when the female glofish tetra gets pregnant. After few days you will find small jelly-like eggs in the tank.

This is just a layer of information on the egg layers glofish tetra, let’s dive into the depth about the pregnancy in glofish.

In this article, I will help you to understand the what, the how, the when, and the why related to the pregnant glofish tetra.

How to Tell if your Glofish Tetra is Pregnant?

First of all, Glofish tetras like any other tetras are egg layers, so technically they can’t get pregnant. Livebearers like guppies, mollies, etc. can actually get pregnant.

The egg is fertilized inside the body of the livebearer whereas egg layers like glofish tetra only carry the egg.

The eggs after females lay them are fertilized externally by the male glofish tetra and hence you can call the egg carrying phase pregnancy.

Although it is wrong to term the egg carrying and laying stage pregnancy, we can suppose it for now. So, here is how you can detect whether your glofish tetra is pregnant or not.

Differentiate The Gender

Okay, hands down, this is the hardest step of all; glofish tetras show no sexual dimorphism until adulthood so it is nearly impossible to differentiate the gender.

Let me help you here although it is not that easy, this advice will help you to some extent. Wait till they reach their sexual maturity.

You can’t differentiate the sex of glofish tetra beforehand. So, when they hit maturity i.e., 4 to 6 months after their birth, follow the instructions and look for the signs I will point out below for you:

  1. Illuminate the tank with glofish tetras with GloFish Cycle Light From Tetra or All Glass Aquarium Fluorescent Strip Light.
  2. Clean the tank so you can clearly see the glofish tetras.
  3. Look for the secondary line along to the blue strip which is the primary line.
  4. If the secondary line is golden, then the glofish tetra you are looking at is male.
  5. And, if the secondary strip is silver, then that’s your female glofish tetra.
  6. Furthermore, look at the shape and size of those glofish tetras.
  7. Females usually have a rounded, pot-bellied look whereas the male glofish tetras are slimmer.

You might like to read a full article on Sex Of GloFish Tetra: How To Tell If Your Glofish Tetra Is Male Or Female?

Swollen Belly

Now, when you know which one of your glofish tetras is female, look closely at them to see if they have a rounder belly.

Although it is their signature feature to have a round belly, the belly grows slightly while she is carrying eggs.

So, compare the before and after size of glofish tetras especially those females to be quite certain about the pregnancy.

Courting Behavior

Once the female glofish hit sexual maturity, she releases pheromones to begin the courting or spawning behavior.

Consequently, the male glofish tetra then releases gonadal pheromones to cause ovulation in the female glofish tetra.

If you see the male glofish tetra chasing the female ones, understand that they are pursuing her to lays eggs.

After few days of all this, you will see tiny jelly-like clutches of eggs in the bottom of the tank.

Is The Glofish Tetra Just Fat Or Pregnant?

People often mistake overweight and obesity as pregnancy in these glofish tetras, so there is the slightest chance that your tetra is just overweight not pregnant.

Overfeeding, the very trait of tetra, is also present in the genetically engineered glofish tetra. Well, they could not change that, do they?

Along with many traits, overfeeding, the love for food, and not knowing when to stop eating are probably still in your glofish.

Try researching the accurate diet for your glofish tetra and follow the instructions there. If they lose weight within few days, you’ll get your answer.

Also, the water parameters play a huge role in bloating fish or making fish fat. You can try to test the water with and maintain the parameters ideal as soon as possible.

Is The Glofish Tetra Sick Or Pregnant?

Another reason for the swollen tummy of glofish tetra can be because they are sick. There are many diseases that clearly shows swollen belly as one of its symptoms.

People often confuse it with pregnancy in glofish; however, in reality, their glofish is actually dying.

Poor water quality with high ammonia content and high level of nitrite can bring so many diseases in Tetras including dropsy. Learn more about Tetra Fish Diseases and Treatments.

Dropsy when triggered by these factors shows its symptom as swollen belly firstly which is then mistaken as pregnancy in glofish.

There is no cure for dropsy but not contagious to other fish in the tank, so there is your silver lining.

Also, make sure the water parameters are ideal and accurate and try changing the water before the case gets out of hand.

Look closely at both male and female glofish, if both of them are showing the symptom, then you are in trouble.

Or else, test the water and if the water parameters are okay and only female glofish tetra has swollen belly then it might be pregnant.

Prepare to take care of the eggs and fry of glofish tetra.

Things To Do When Your Glofish Tetra Is Pregnant: Breeding Requirements Of Glofish Tetra

Once you are sure about the eggs in the female glofish tetra, you have to provide the necessary things to ensure their safety.

Let me point out some major things to look at when your glofish tetra is carrying eggs:

Filtration Of The Breeding Tank And The Aquarium Nitrogen Cycle

Although the breeding of glofish tetra is unintentional, you need to make sure they are getting everything appropriate when the female is carrying eggs.

Filtration, as well as the aquarium nitrogen cycle, are two important factors that decide the survival of pregnant glofish tetra and their eggs.

Clean water with no presence of ammonia and nitrite is what these tetras ask for in the tank. Learn more about How to Clean a Tetra Fish Tank? [Step-by-Step].

Glofish tetras are weak and vulnerable when they are carrying eggs like any other living being.

The slightest change and carelessness can become the death of female glofish along with the eggs inside them.

You might like to read a full article on Types of Aquarium Filter For Tetra Fish and Filtration Methods.

Heater In The Breeding Tank

In the breeding tank or say the tank where glofish are supposed to lay eggs, the temperature needs to be 78°F.

Temperature plays quite an important role in the survival of tetra be it glofish or any other tetra.

And the pregnancy phase can be tiring and weakening, so temperature change can bring diseases and problems in the glofish.

Aqueon Pro 100 Submersible Aquarium Heater will be ideal for your tank with glofish. You can easily find and order this heater on and from amazon respectively.

Diet For The Glofish Tetra

The nutritional value of the food you feed your glofish tetra must be accurate to the nutrients their body asks.

You can’t compromise the health of these tetras by feeding them less or inappropriate. With healthy and nutritional diets, your glofish will lay eggs and the fry developing from them will be healthy too.

Tubifex to frozen brine shrimps along with the commercial flakes, you can make a proper diet plan for these tetras.

How Often Do Glofish Tetra Lay Eggs?

Well, during the breeding season, which is the rainy season for most tetras, glofish tetras are quite active sexually.

So, there is a high probability of seeing many clutches of eggs within the interval of few days.

The female glofish tetras when hit maturity, have the capacity to lays eggs every two to three days.

Thus, by the end of the rainy season, you will find hundreds of eggs in the tank along with the fry.

I have also written an article on How Often Do Glofish Lay Eggs? Have a look!!!

How Many Eggs Do Glofish Tetra Lay At Once?

I mentioned in the above section about the frequency of egg-laying in female glofish tetra. But it is equally important to know how many eggs should you be expecting each time they lay eggs?

This will make it easier for you to prepare yourself mentally while making the preparations for new baby tetras to arrive.

When a female glofish tetra releases the eggs, you will see a clutch of several hundred eggs each time.

If only all of them would fertilize, hatch, and develop into new glofish tetras, it will be a nightmare for you.

What Do Glofish Tetra Eggs Look Like In A Tank?

When you see your male glofish tetra following and chasing your female glofish tetra, be ready to see eggs in the tank.

But what should you look for? Are their eggs colorful like their body? Sorry to say but eggs will have no such color and it will be quite hard to pinpoint the location of eggs.

However, the color will retain in the fry when they start to develop. So, don’t worry about it. Now back to the topic.

The glofish tetra’s eggs are transparent and are white or slightly yellow. These eggs look like tiny cream or whitish orbs in the tank.

However, it can be hard to see unless you are attentive and observant enough or it will be easier if you have a black substrate in the tank.

These eggs seem to be in a clutch together and are most often eaten by parents glofish. You need to take correct precautionary measures to save the egg before they hatch.

Furthermore, you need to keep Java moss as it helps you to identify eggs easily. These eggs look like a tiny grain of sand lying on the Java moss.

You can buy Java Moss Portion in 4 Oz Cup – Easy Live Fresh Water Aquarium Plants from amazon.

How Long Does It Take For Glofish Eggs To Hatch?

After the female lays the eggs, the male glofish tetra fertilizes it immediately. Once the egg is fertilized, you will see a black dot inside it.

The black dot in the egg suggests successful fertilization whereas its absence suggests unfertilized eggs.

After all this, you have to wait for few days, 2 to 3 days to be precise, for these eggs to hatch.

But the fry will take some time to come out of hiding so wait for few more days to see new babies of glofish tetra.

You need to make sure the tetra fry tank is well-filtered and clean with no presence of ammonia or nitrite.

Here is an article to guide you about Aquarium Filters Best Suited For Tetra Fish Fry

How to Save And Care for Glofish Tetra Eggs?

Saving the eggs of glofish tetra can be quite tough as glofish eat its eggs and have no parental instincts. The male might fertilize the eggs immediately but it will also eat them with no remorse.

So, it comes down to you saving the glofish tetra eggs as well as caring for them before and after they hatch.

Firstly, like many other aquarists, you can add marbles which can give space to these small eggs to slide into.

Glofish fry can easily get out of the gap when they hatch from the egg. But the wisest thing to do is to remove the parent fish out of the tank.

Also, keep Java moss in the tetra tank; this specific plant will give space to hide the eggs as well as the newly born fry.

Frequently Asked Questions

You might have few more questions lingering in your mind so let me help you. Here are answers to few FAQs on glofish tetra that might help you.

Is Glofish Fertile?

Yes, Glofish is Fertile. Although there is a huge war going on this very topic as some aquarium enthusiasts highly speculate that the glofish are supposedly made infertile.

However, this is not the case as glofish are no doubt fertile and can lay eggs when the female mates with male glofish.

Even in the captive situation, if both male and female are present, there is a chance of seeing eggs as well as fry in the tank sooner or later.

Is It Illegal To Breed Glofish?

Yes, it is illegal to intentionally breed, barter, or trade glofish tetra as the license and copyright to do that legally belongs to the GloFish Company.

The GloFish Fluorescent Fish License strictly states “Intentional breeding and/or any sale, barter, or trade, of any offspring of GloFish fluorescent ornamental fish, is strictly prohibited.”

Glofish is a patent breed and hence the company covers the selling and reproducing of any type of glofish.

You will be punished according to the law if you are found breeding or selling these fish intentionally.


In conclusion, glofish tetras might be illegal to breed but you have no say in the natural phenomenon. Even if you want to stop breeding and spawning, you will have a hard time separating male from female. And when there are two genders of glofish tetras present in the tank, it is quite impossible to stop the female from laying eggs or the male from fertilizing them. All you can do is contemplate if your glofish are pregnant or not and act accordingly. Try to give a favorable environment for the development of new baby glofish tetras. But never try to sell them neither to the pet store nor to the local fishkeeper: it is illegal.

Although ‘the more the merrier’ but here it can be a nightmare caring for so many glofish tetras at once. You know neither all the eggs are fertilized nor all the fertilized eggs hatch. So, the minimal survival rate of both eggs and fry makes it easier for you to prepare for fewer new ones.

You will do a good job until and unless you follow my instructions. And if there is something you want to ask; remember I am just a comment away.

Good Luck!!!

Happy Fish Keeping!!!

Recommended Articles:

  1. Breeding Tetra Fish – Step By Step Guide
  2. Tetra Fry Tank Set-Up: Fish Tank Requirement For The Fry
  3. How to Set Up Tank for GloFish: Beginner’s Guide
  4. How To Feed Tetra Fish Fry Properly | Dos & Don’ts With Alternative Food


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