Eliminate Your Fears And Doubts About Pregnant GlowFish

Do you want to know how to tell if your Glowfish is pregnant and what to do if they are pregnant? Don’t worry, we have covered everything to help you navigate the mysteries of pregnant Glowfish and make sure their babies have a healthy and safe start.

Genetically Glowfish is a modified version of zebra danio. It is enhanced with the genes of unrelated breeds. These futuristic and beautiful species have fluorescent scales which glow under a black light. Glofish is a very popular breed, but also controversial.

If you are highly interested in pregnant Glowfish breeding, remember that legally you can not sell this fry. Glofish is a patented species, so the company that initially created the breed has the right to sell it. Breed the Glofish only if you have the available space to keep lots of glowing adult danios. My suggestion is no to release Glowfish into the wild.

Pregnant GlowFish
Image Source: LiveAquaria

Follow these steps if you are prepared to breed Glofish

1. Find a healthy pair of Glofish for breeding. If you are a newbie then you can try starting with a single male and two females. Males have narrow and slim bodies and female Glofish are round and plump in shape. They should be mature, active, and young; a perfect time to start trying to breed your Glofish is when they have attained 3/4 inch in its total length. You should only breed Glofish of the same color and size.

2. High-quality foods are to be Feed your Glofish such as daphnia, frozen brine shrimp, tubifex, and commercial flakes. If your glo fish have eaten a healthy diet prior to conception then they will be able to breed much more prolifically.

3. A well-cycled breeding aquarium of at least 3 gallons is to be used while placing your pair. The tank’s substrate should be either smooth marbles or gravel; these give crevices for the laid eggs to land so that the parent Glofish will not eat those eggs.

4. Observe the Glofish in your tank for several hours for breeding signs. In an established aquarium, usually the breeding pair will start chasing each other and engaging in spawning embraces.

5. After passing several hours of observation, take the adult Glofish out of the aquarium and test the substrate for eggs. They might be so tiny that you won’t be able to see them.

6. Watch your aquarium carefully for the next 45 – 50 hours. If the breeding of Glofish was successful, then after about a day there should be fry. The babies are extremely small and cling to the sides of the tank.

7. When your Glo fries are free-swimming after a few days, you can start to feed them commercial fry food. Usually, these are fine liquids or powders that give near-microscopic particles which the baby Glofish can easily consume. Feed as per the instructions of the manufacturer.

8. Your tank’s water parameters should be checked three times every week. Keep your aquarium’s ammonia levels undetectable, and don’t permit the nitrate levels to increase above 10 ppm. Otherwise,  your newly-hatched Glo fish fry will be lost forever.

9. When your Glofish fry reaches 2 weeks of age, start feeding ground flake food. After reaching one month of age, their water requirements and care are exactly the same as adults.

10. Don’t forget that you should provide new tank’s after breeding the Glofish. Under no conditions or circumstances is it acceptable to sell Glofish to  private fishkeepers or pet stores. It is considered as a criminal offense (also considered as potential ecological disaster) to release Glofish into streams or wild ponds.

How to know if a Glowfish is Pregnant

Pregnant GlowFish

Glofish are one of my favorite aquarium occupants because of their futuristic look and bright colors. They are easy to care for. However, it is quite tricky to breed them since the female glo fish looks perpetually pregnant, and also the parents will often eat their own eggs before you even see they’re present there.

What Does a Pregnant Glowfish Look Like?

You can distinguish female and male Glofish apart based on their look: the male Glofish have a slimmer body while the female Glofish are more rounded and look pot-bellied. Often their natural appearance can make your female Glowfish look pregnant when they’re actually not.

To be more accurate, the female Glofish never gets pregnant. Female Glofish are not live-bearing fish. Alternatively, they carry and lay eggs after mating. Technically speaking, if animals are carrying live young then they are considered as pregnant. But, the word “pregnant” is not used frequently to refer to an animal or fish who is carrying and ready to lay eggs, that is why I as an aquarist– along with most of the participants in the fish keeping community – still use the word “pregnant” while referring to Glofish.

A pregnant Glowfish looks slightly more rounded than normal when she is ready to start laying her eggs. It is very hard to determine if a Glofish is pregnant by looking at her appearance, therefore you have to rely on behavioral cues to some extent.

 How Long do Pregnant Glo Fish Carry Eggs?

Pregnant glowfish develops their eggs once they become sexually mature which is generally when their body size is about 3/4th of an inch long. As and when your female Glofish is pregnant, after engaging in mating rituals they just wait to lay their eggs in the presence of male Glofish. This includes chasing one another around an aquarium and performing “spawning embraces” in which both males and females press close to each other and seem to vibrate or wiggle together.

After eggs are being laid for the first time, more eggs are developed by the females and carry them until the eggs are ready to lay again. Therefore the pregnant glowfish are almost always carrying eggs.

How Often Do GlowFish Lay Eggs?

GloFish or glowfish come in different vibrant fluorescent colors such as green, red, orange, blue, pink and purple. Genetically they are engineered zebra fish, also known as zebra danio fish. A naturally occurring fluorescence gene is placed by Scientists in the zebra danio fish, which finally resulted in various vibrant colored fish seen today. Nowadays GloFish can be bred without the help of any scientists. Their beautiful vibrant color is inherited from their parents and it is continued to pass on to the future generations.

Egg Production and Courtship Frequency

When pheromones are released by female GloFish then it initiates courtship behavior in the male fish. The pheromone released by male is called gonadal pheromones, which causing ovulation to occur in the female Glofish. Females have the capacity to lay eggs at the interval of every 2 – 3 days. An individual clutch can have up to a few hundred eggs.

Signs of Eggs in a Female GloFish

The pregnant Glofish will show some physical behaviour that eggs are being carried by them. The most noticeable symptom is a swollen belly. A lot of newbie pet owners confuse the swelling of the abdomen with pregnancy which is not actually true. In reality GloFish are not live-bearers. So GloFish can not be said to undergo pregnancy. The females release eggs in the presence of male GloFish.

Fertilization of Eggs

Eggs are released by female GloFish by dropping them into the water, generally as they swim throughout the aquarium or at a spawning site. Once the female GloFish releases their eggs into the tank water, the males start to fertilize the eggs as they fall to the bottom of the aquarium. Eggs from one female can be fertilized by multiple males.

Survival of Eggs

The fertilized eggs survival is minimal. Most of the fertilized eggs are eaten by the adult GloFish immediately after laying eggs. My suggestion is to add some marbles to the bottom of your aquarium to protect the fertilized eggs. The marbles you added leave some small gaps open for the fertilized eggs to slide into or bounce, where the eggs are shielded. To hatch the eggs it takes upto 2 days. Finally it takes again another 2 to 3 days after that for the glow fry to swim out in search of their food.

What You Need to Know About Glofish Eggs and Its Fry

The eggs of GloFish are incredibly small. The adults like to eat their eggs. So you have to take some necessary steps to make sure that the eggs survive and their babies – which is called fry – get a healthy beginning.

First and foremost thing is to keep notice and observe the behaviors of the fish to see if they initiate exhibiting any mating signs. If you have healthy and young Glofish who don’t look interested in mating rituals, then feed your adult fish some high-quality food. When your female pregnant glowfish is looking rounder than usual, move them to a well-established mating tank that only contains a few inches of water or  change 50% water of your tank. Often this encourages spawning, which is when the female GloFish releases her eggs which will drift to the bottom of the aquarium where these are fertilized by the males.

In your tank, you will want to place gravel, marbles, or a slim grate-like sheet in the bottom of your aquarium. It will offer a safe haven for the expelled eggs to drift down into where the adult fish won’t be able to consume them. 

As and when the eggs are laid and fertilized, generally they hatch after almost 24 hours. Then the tiny fry will take extra 24 hours to start emerging from the marbles or rocks. At this stage they are so small that you would not be able to see them with empty eyes.

Once the fry is able to swim freely in the aquarium – normally it takes 2 or 3 days after they hatch – you can feed your fry with commercial food. This food is very powdered food which is sufficient for your fry to consume with a lot of nutrients to help them grow.


If you are wondering and eager to know how to tell if a Glofish is pregnant, then the answer is very simple: There are some sort of chances that your female Glofish is already pregnant!

Most pregnant Glowfish spawns quite frequently and easily when they are kept in a clean tank and are well-fed.

If you want your small fry to live long, place some kind of rough substrate or marbles in the bottom of your aquarium to hide the eggs from the adult GloFish, and you will see little baby Glofish swimming around the aquarium in no time at all!


Dibyajyoti Bordoloi is the creator and author of FishCampRehab.com, a third-generation experienced fish keeper and owner of a successful pet breeding farm. He is also a member of the Center for Wildlife Rehabilitation And Conservation (Assam), the Marine Aquarium Societies of North East India, and the Kaziranga Nature Conservancy of Assam.

Leave a Comment