How To Tell if Betta Eggs are Fertilized

If you plan on breeding your bettas, it’s essential to understand the betta breeding process and know how to identify fertilized betta fish eggs. 

Once your female betta fish lays a batch of eggs, the process has only begun.

You must determine whether the eggs are fertilized based on their appearance, maintain the ideal temperature and other parameters in the betta tank, and check the eggs for signs of hatching. 

It’s possible to tell if betta eggs are fertilized by the obvious gray spot in the center of the egg. This is the baby betta growing. You’ll also notice a daily size increase which you won’t see if the eggs are unfertilized.

how to tell if betta eggs are fertilized atf

How Long Until You Know If A Betta Egg Is Fertilized?

You won’t be able to tell immediately whether the eggs are fertilized.

After a betta pair has mated, the hatching process typically takes three days.

You must monitor the eggs during this time to watch for signs of fertilization.

If the eggs do not change in appearance over three days, it means they’re most likely unfertilized. 

When determining this, there are several key characteristics, as fertilized betta eggs look different than unfertilized eggs. 

Characteristics of Fertilized Betta Eggs

Fertilized betta fish eggs may be a yellow or brownish color, and they often have two gray or black spots visible.

The eggs will be clear enough to see inside and will feature a slit on the surface.

The slit is where the male betta fish fertilized the eggs, and its presence is a sure sign the eggs have been fertilized successfully. 

Another way to identify fertilized betta eggs is to see whether they float or sink to the bottom of the aquarium.

Fertilized eggs will sink, after which the male betta will place them into a “bubble nest” he’s made for safety. 

Differences between Fertilized and Unfertilized Betta Eggs

fertilized betta egg signs

If a betta pair has failed to produce fertilized eggs, the eggs will have specific characteristics which become evident in the following days:

  • Opaque, rather than clear
  • White in color
  • No fertilization slit present
  • Float to the top of the tank

If the betta eggs still align with these characteristics after a couple of days, it’s likely the eggs are not fertilized.

This is because fertilized eggs constantly evolve to show the betta fry growth before hatching. 

ColorBrownish or yellowishWhite
Clear or OpaqueClearOpaque
Floats or SinksSinksFloats
Gray SpotsYesNo
Fertilization SlitYesNo

The behavior of the male betta will also be different if the eggs are unfertilized.

Rather than acting protective towards the eggs, he will likely ignore or dismiss them.

The Fertilization Process

Betta eggs undergo a specific fertilization process, and for the eggs to hatch, the aquarium must be within optimal temperature parameters. 

Overview of the Fertilization Process

During breeding, a betta pair works together to create fertilized, viable betta fish eggs. 

Female betta fish lay the eggs, which they keep for approximately two weeks in their ovipositor tube before releasing them. 

Male bettas are responsible for betta egg fertilization, and they do this by releasing sperm over the eggs. Within hours of the sperm being released, the eggs become fertile.

Once the male has fertilized the eggs, he will move them into the safety of a “bubble nest.” 

Learn more about bubble nests in our dedicated article at the link.

On average, the hatching period for betta fish eggs ranges from 2 to 3 days.

Egg hatching may take longer if the temperature in the aquarium is too cool.

If this is the case, investing in an aquarium heater may be ideal to ensure the successful hatching of the betta fish eggs. 

Of course, there are situations where the sperm fails to fertilize the betta eggs. This is usually due to factors such as water temperature, water quality, and the age and health of your bettas. 

Water Temperature 

betta egg water temp

The warmer the water is, the faster the fertilized eggs will hatch.

The ideal water temperature for betta eggs is 76-82° degrees Fahrenheit (28° C).

Keeping the water below this temperature range can result in an extended hatching period or in failure to hatch. 

Please note: this is a little higher than what we recommend for the standard adult betta, which should only top out at 80° degrees Fahrenheit (27° C).

If you’re keeping the fish AND the eggs in the same tank, be wary.

We recommend having a separate tank for fry care and egg incubation.

These small discrepancies in the water can make a difference in the health of both fish and egg.

Plus, the adult betta have been known to eat their young on occasion.

Water Quality

Bettas require specific water parameters to thrive, and the same is true for their eggs.

Keep your bettas’ aquarium water within the following parameters to ensure the betta eggs hatch successfully: 

  • pH: 6.5 to 8
  • Oxygen: 5 to 7 ppm

It’s also essential to keep ammonia and nitrate levels as low as possible and to regularly test the water for the presence of heavy metals.

Large enough quantities of these harmful substances can kill your fish, especially if left untreated for a long time.  

To maintain the water quality of your betta aquarium, perform frequent water changes and test the water regularly. 

Betta Age and Health

Healthy bettas produce more viable eggs and have more success in fertilizing them than unhealthy bettas.

It’s a good idea to monitor your bettas’ health status regularly.

Parasites, as are diseases such as dropsy, are common in freshwater aquariums.

For a complete list of betta diseases, check out our article.

Age also plays a role in successful betta breeding, with bettas past their prime laying or fertilizing fewer eggs.

Bettas reach sexual maturity at around 3 months old, meaning they can mate and breed. 

Watch for common signs and symptoms; something may be wrong with your betta: 

  • Flashing behavior
  • Color dulling or fading
  • Clamped fins
  • Lack of appetite
  • Lethargy or lack of energy
  • Visible issues with the gills or skin

If you notice any of these symptoms in your bettas, get a proper diagnosis from a vet and begin caring for your sick fish. 

Observable Signs of Fertilization

betta egg dot

Fertilized betta fish eggs tend to sink toward the bottom of the aquarium, and the male betta places them in the safety of a “bubble nest.”

If a betta egg is fertilized, it will meet the following criteria: 

  • Has a brownish or yellow color
  • Has a fertilization slit present
  • Features two gray or black dots
  • Shows signs of growth over time

Another sign of successful fertilization is the behavior of the male betta, which will act protective toward the nest and eggs.

This may present as the betta becoming more aggressive than usual with other bettas in the aquarium.

Male bettas are also known to watch the nest, scooping eggs back into the nest if they fall out. 

Incubation and Hatching

The average time it takes for betta eggs to hatch is within three days of fertilization.

However, this timeframe can be shorter or longer based on the water temperature.

Warmer temperatures promote faster hatching, whereas colder temperatures slow down the process.

Once the eggs have been fertilized, monitor their progress every several hours. If all is well, you will see signs the eggs are growing and preparing to hatch.

As the eggs get closer to hatching, you may see the fry wiggling around inside the eggs. 

To ensure the betta eggs hatch successfully, keep your aquarium’s water within optimal incubation parameters: 

  • Temperature: 76-82° degrees Fahrenheit (28° C)
  • pH: 6.5 to 8

In addition to keeping oxygen levels high and ammonia levels low, this will create the perfect environment for the betta eggs to hatch. 

Anticipating Baby Betta Fry

It’s crucial to understand how the fertilization process works, identify fertilized versus unfertilized eggs, and create an optimal environment for incubation and hatching. 

Fertilized betta eggs may be brown or yellow in color, have a fertilization slit present, and sink to the bottom of the aquarium.

They may also have two black dots visible, signifying successful fertilization. 

For more on the betta breeding process, check out this article.

How useful was this post?

Click on a star to rate it!

As you found this post useful...

Follow us on social media!

We are sorry that this post was not useful for you!

Let us improve this post!

Tell us how we can improve this post?



Wesley Oaks has a background in web publishing and decided to combine his skillset with his enjoyment of betta fish. When he isn’t working behind the scenes for Betta Fish Bay, he’s homeschooling his kids and soaking up quality family time.

Follow Us on Facebook!

Get betta fish fun facts right on your Facebook feed and see when we share new content by following our page on Facebook.

blue betta fish

Advertiser Disclosure

We are reader-supported and may earn an affiliate commission when you buy through links on our website. To be 100% clear, you should assume that we will earn a commission on any product you purchase after clicking on links or images on this website.

Our affiliate partners include but are not limited to

In addition, we generate revenue through advertisements within the body of the articles you read on our site.

Although we only recommend products that we feel are of the best quality (which we may or may not have personal experience with) and represent value for money, you should be aware that our opinions can differ.

A product we like and recommend may not be suitable for your unique goals. So always be sure to do your due diligence on any product before you purchase it.