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How Do Betta Fish Eggs Get Fertilized?

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As an aquarist who loves betta fish, one of the questions I kept asking myself was how do their eggs get fertilized. Fortunately, after years of experience, I gained some knowledge on this topic. I also learned what steps I should take to ensure that the eggs get fertilized properly.

After the female has done producing unfertilized eggs internally, the male betta squeezes her, forcing her to push them out. Then, as they are released, the male will produce milt containing its sperm, fertilizing the eggs.

As we move forward, I will elaborate on how betta fish eggs get fertilized. Then, I will discuss whether bettas can lay unfertilized eggs and what steps you should take to ensure the fertilization goes smoothly.

Still curious? Feel free to check my complete guide on betta fish eggs. There, I discussed how to care for betta eggs, what they look like, how long it takes for them to hatch, what equipment to use, and much more.

How Do Betta Eggs Get Fertilized?

If your tank has ideal conditions, bettas will breed with relative ease. However, your betta population will not grow unless you have fertilized eggs that can hatch into healthy fry.

If you’re new to betta fish, some aspects of their breeding process may surprise you:

1. The Female Produces The Eggs Internally

First of all, you cannot breed bettas unless you have both genders. The females do not fall pregnant, not in the conventional sense. Instead, they produce eggs internally.

You need a male fish to fertilize those eggs once they escape the female betta’s body. You can’t afford to maintain a tank with just one gender, not if you want your betta population to grow.

2. The Male Betta Courts With The Female

Courtship precedes fertilization. Female fish can produce eggs without a male betta. The primary purpose of the male betta is to fertilize the eggs, but only after the female has generated them internally.

Female bettas with eggs will manifest certain signs, for instance:

  • Look for vertical stripes on the female. These stripes are normally white, but you may observe a different color. The stripes prove that the betta is producing eggs.
  • Fertile bettas have a dot on the stomach. This dot reveals a section called the ovipositor where the eggs fall after the fish makes them. You will probably see a white tube. But for some people, it looks like a white dot. Either way, it proves that the fish is releasing eggs.[1]
The female betta fish ovipositor is seen in the lower part of the abdomen.

Look at the male fish if you can’t see any dots or stripes on the female betta. Is it making bubble nests? Bubble nests appear in the wild as well. You cannot miss them in an aquarium. Clusters of tiny bubbles tend to stand out.

The male betta makes these nests on the surface or under debris. Their presence shows that the betta is fertile and more than ready to mate.

Fertile females will respond to the bubble nests, paving the way for a courtship routine that occasionally looks like fighting.

The size of the bubble nest doesn’t matter. Some people think that larger bubble nests attract more females because they signify strength and dominance.

But studies have disproven this theory. Male bettas with larger nests are not necessarily more effective at securing female partners.[2]

3. The Male Squeezes The Eggs Out

Labor among bettas is bizarre. The female makes the eggs internally, but it doesn’t push them out. Instead, the male fish wraps itself around the female. Then it squeezes the female, forcing the eggs to pop out.

The female may drift momentarily as if stunned. Female bettas lay roughly 30 to 40 eggs. Though, that number can jump up to 400 or even 500 eggs under the appropriate conditions.[3]

But the female doesn’t push them all out at once. The male betta can spend up to a day squeezing the eggs out of the female.

4. The Male Fertilizes The Eggs

Once the eggs are free, the female betta’s role ends. At that point, the male betta takes over completely. The creature is responsible for the health and safety of the eggs. It safeguards the offspring by carrying them to the bubble nest.

Fertilization can take place during or after labor. Many aquarists will tell you that their male bettas generate the milt and fertilize the eggs as the female releases them. In other words, the male fish is still wrapped around the female.

But some aquarists have seen their male bettas fertilize all the eggs after the females have released them and departed.

Either way, the results are the same. The male fish will look after the eggs in the nest, retrieving those eggs that occasionally fall out and taking them back to the nest.

The female is a threat to the babies during this period. If you take the male betta out of the tank, the mother will probably eat the babies.

Can Betta Fish Lay Unfertilized Eggs?

What if your tank lacks a male betta? What then? Well, the female betta is still capable of laying eggs. But this is rare. You can always find eggs inside a female betta. However, it usually keeps them contained until it finds a viable mate in the aquarium.

If the water conditions are harsh, it may even re-absorb the eggs. But on occasion, the female will release the eggs into the aquarium, especially if it has a clean environment, the correct parameters, and a high-quality diet.

The key is a conducive breeding atmosphere. It encourages the mother to push the eggs out instead of re-absorbing them. This is more likely to happen if the female recently mated because it has been conditioned to release the eggs.

But eggs in an aquarium that doesn’t have a male fish are pointless. Without the male betta’s milt to fertilize them, the eggs will rot, adding ammonia to the water. You should remove them as soon as possible.

Admittedly, many mothers will simply feed on these eggs. This also applies to other aquatic creatures, such as shrimp, frogs, etc. To them, eggs are considered food.

But you can’t trust betta fish to keep the tank clean. The eggs will most likely sink to the bottom, so you have to vacuum the substrate.

If you don’t have the time to vacuum the substrate, add more female bettas. This will increase the chances of the bettas eating the eggs.

How Do I Ensure The Eggs Get Fertilized?

First of all, you must have a male betta in the tank. As mentioned earlier, some females will lay eggs without a male, but they will never be fertilized. Most people breed betta fish by introducing one male to one female.

But you can also introduce a male betta fish to a female sorority. Either way, avoid rearing more than one male betta fish in a tank, as they are too aggressive.

The next step would be to adjust the water parameters for betta fish. A suitable water environment will reduce stress and ensure that the fish reproduce efficiently.

These are the water parameters you should aim for:[4]

  • Temperature: 78-80° F (25-27° C)
  • pH: 6.8-7.5
  • Hardness: 5-20 DH (70-300 ppm)
  • Ammonia: 0 ppm
  • Nitrites: 0 ppm
  • Nitrates: <20 ppm

To measure the ammonia, pH, nitrates, and nitrties, I personally use the API FRESHWATER MASTER TEST KIT (link to Amazon). After trying dozens of testing kits, that is probably the most accurate. It also lasts for about eight hundred measures, so it is highly cost-effective.

I also suggest picking a breeding tank that is long but not tall. Wide tanks will allow the male betta to build an efficient bubble nest with plenty of oxygen. Tall tanks are problematic on this matter.

Can The Fertilized Eggs Survive Without A Bubble Nest?

You don’t need bubble nests to rear bettas. They are vital to the health of the eggs. But that is mainly because a bubble nest provides protection. Additionally, because bettas build bubble nests on the surface, the eggs have plenty of oxygen.[5]

But the nests have nothing to do with fertilization. The male fish produces milt to fertilize the eggs as the female releases them. Once the eggs are fertilized, you can sit back and wait for them to hatch two or three days later.

It may take a month if you have mouthbrooder bettas.[6] But ultimately, if you have a clean tank with the appropriate conditions, the offspring will survive with or without a bubble nest. Some eggs even hatch on the bottom of the tank.

The best option is to allow the male betta to create bubble nests. But if you had to remove the male fish for one reason or another after it fertilized the eggs, they would still hatch.

If you found this article helpful, these may also interest you:

Pro tip: If your betta fish has just laid eggs, you’ll need to know what to do with the fry. For that, feel free to check my complete guide on betta fish fry.


Like many other types of fish, bettas first produce unfertilized eggs. Only after their secretion does the male release sperm that is absorbed and fertilizes the eggs. The timing in which this happens is still controversial.

Most aquarists argue that the male fertilizes the eggs as soon as they are being popped out. However, some believe that only after they sink to the bottom the male hovers above them and releases its sperm.

Either way, the male will take care of the eggs. After fertilizing them, he will build a bubble nest to ensure the fry get enough oxygen, although that isn’t mandatory.