How To Tell If Betta Eggs Are Fertilized? (With Pictures)

Disclosure: When you purchase something through my affiliate links, I earn a small commission. As an Amazon Associate, I earn from qualifying purchases.

I remember how excited I was when I saw my female betta fish secreting her eggs. I even caught the male collecting the eggs into the bubble nest he had carefully built. But how could I know if the eggs were fertilized? Could it be that all the hard work was in vain? Luckily, as time passed, I gained some experience in the field.

These signs indicate that your betta fish’s eggs are fertilized:

The eggs develop yellowish or brownish shades.

The eggs grow slightly.
Two black dots appear, resembling the fry’s eyes.
The male betta will care for the eggs.

The eggs eventually hatch after three days.

As we move forward, I will elaborate on how you can determine whether your betta fish’s eggs are fertilized. Then, I’ll discuss what steps you should take if the eggs don’t hatch after 72 hours as they should.

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 To Tell If Betta Eggs Are Fertilized?

A betta fish begins life as an egg cell that undergoes several drastic transformations until the embryo forms and the egg hatches, adding betta fry to the water.^[1]

But a male fish has to fertilize the eggs before they can hatch. Female bettas do not fall pregnant.^[2] You can only call a fish pregnant if it has live fry or fertilized eggs in its belly.

Betta eggs are fertilized outside the body, which is why aquarists use the term ‘Gravid’ instead of ‘Pregnant’ to describe fish that are heavy with eggs.

The following signs tend to differentiate fertilized eggs from their unfertilized counterparts:

1. The Eggs Develop Yellowish Shades

Betta eggs are white and oval-shaped at the start. But over time, they will become yellowish or brownish. They will also develop gray spots.

Unfertilized eggs usually remain white, at least in the beginning. Over the next few days, they will become opaque as the shells develop fuzzy growths, proving once and for all that they were not fertilized.

An image demonstrating fertilized betta fish eggs on the right and unfertilized eggs on the left

2. They Will Grow A Little

It takes betta eggs three days to hatch. As such, they don’t change size as dramatically as eggs from other species that require several days and weeks to hatch.

However, a fertilized betta egg will grow slightly. This change may go unnoticed by new aquarists that know little or nothing about fish.

But if you have experience with bettas and their eggs, you will notice the size difference. Unfertilized eggs don’t change because they don’t have any embryos growing on the inside.

3. You Can See The Eyes Of The Fry

Fish eggs are technically translucent. Therefore, if you observe the eggs closely, you will see the fry and their yolk sack inside.^[3]

If you can’t see the babies, look for the eyes. They look like two black dots inside the egg.^[4] This is a tangible sign of fertilization. Unfertilized eggs are opaque. They have nothing to show you.

Some of the betta eggs show two black dots that demonstrate the fry’s eyes

4. The Male Betta Takes Care Of The Eggs

The female betta doesn’t raise her offspring. In fact, she tends to eat them, which is why aquarists remove her the moment she pushes the eggs out.

The father remains because he has to care for the eggs, using his mouth to carry them to the bubble nest at the surface of the aquarium.

Bubble nests are somewhat annoying because they can obscure the eggs, making it difficult for aquarists to determine whether or not the female betta laid eggs.

You have to look for white spots among the bubbles. Though, the water can refract the light in a way that makes the eggs look like bubbles.

The eggs are easier to spot once they develop black spots. But even if you can’t see eggs, you can trust the father to protect them. The male betta fans them to remove debris. He also retrieves them whenever they fall out of the nest.

But he only shows this attention to the fertilized eggs. If the tank has unfertilized eggs, the male betta will simply eat them. In a way, he acts as a sieve.

Unfertilized eggs are dangerous because they add ammonia to the water when they rot. You want the father to eat them before they pollute the aquarium.

Admittedly, male bettas do not always behave. They have been known to eat fertilized eggs as well. But in many cases, their actions are driven by external stimuli. The most common being stress and hunger.

Some people don’t want to feed the male betta until the eggs hatch because doing so may compel the creature to eat its offspring.

Others expect the male bettas to eat the eggs if you starve them. They prefer to feed the fish small quantities of food to keep their cravings at bay.

5. Fertilized Eggs Should Hatch After Three Days

One way of identifying fertilized eggs is to wait for them to hatch. Female betta fish can lay eggs without a mate, but unfertilized eggs won’t hatch.

Give it two or three days for the fry to emerge. You can assume that every egg that hasn’t hatched after three days is unfertilized.

What Happens To Unfertilized Betta Eggs?

Unlike the eggs that a fish fertilizes inside the body, male bettas do not fertilize every egg that a female betta pushes out. The sperm in a betta’s gonads is immotile. In other words, it doesn’t move.^[5]

The fish has to release the sperm into the water before swimming toward the eggs. The sperm remain in motion for mere minutes, which isn’t enough time to penetrate all the eggs.

External factors can interfere with the sperm’s operations, including contaminants in the water. Experienced aquarists know that every batch of eggs has a mix of fertilized and unfertilized eggs.

It doesn’t concern them because they know that the bettas will produce more eggs. But the unfertilized eggs cannot stay in the aquarium.

This isn’t a problem if you have bettas in the breeding tank. The females won’t hesitate to eat their offspring, both fertilized and unfertilized.

The father has more self-control. But he will also eat the unfertilized eggs because he knows they are dead. Once the fertilized eggs hatch, you have to remove him. Otherwise, he will eat the fry. But what about the uneaten unfertilized eggs?

If the mother laid 300 or more eggs and at least half of them went unfertilized, the male betta is unlikely to eat them all in those three days before the fertilized eggs hatch, and you have to move him back to the community tank.

However, dead eggs are rarely a challenge for aquarists with a strict maintenance routine. The cleaning process will eliminate them over time. This assumes that you perform regular water changes.

It also assumes that you vacuum the substrate and your filter works. The eggs are just another pollutant your maintenance regiment has to remove. They don’t require special treatment.

If the bettas gave birth in a community tank, the unfertilized eggs would be even less of a problem because the adult fish, shrimp, and snails would eat them.^[6]

If you have sufficient foliage, the newborn fry will hide from predators. You will still lose some of them, but many will survive. On the other hand, unfertilized eggs cannot hide, making them vulnerable to predators.

What Should I Do If The Eggs Don’t Hatch?

As was previously mentioned, if your betta fish’s eggs don’t hatch after three days, they are most likely unfertilized. Most fish owners don’t grow bettas in community tanks because they don’t get along with other fish.

That is why it is less likely that other fish will eat the unfertilized eggs. So, you should intervene before the rotten eggs ruin the water chemistry.

If you see no changes in the eggs after 72 hours, you should take them out. Do that even if it means you are about to ruin the bubble nest your betta worked so hard to build.

Since rotten eggs produce ammonia and nitrates, they will lower the pH and make it difficult for your betta fish to breathe. If your fish produced a large batch, I suggest that you test the water parameters.

To do that, I personally use the API FRESHWATER MASTER TEST KIT (link to Amazon). This bundle will accurately measure the pH, ammonia, nitrates, and nitrties. It also lats for eight hundred measures, so it is highly cost-effective.

The ammonia and nitrties should be kept at 0 ppm while nitrates are below 20 ppm. The pH should be between 7.0 and 7.2.

If the toxins are higher than recommended, perform more frequent water changes. That also applies to water that is too acidic. You may also consider getting a water conditioner, like the well-known Seachem Prime (link to Amazon).

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

What Do Betta Fish Eggs Look Like? (With Detailed Pictures)

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.

Conclusions

You can tell that your betta fish’s eggs are fertilized by their general appearance. Fertilized eggs will change their color and develop yellowish/brownish colors. You will also see them growing a little if you observe them carefully.

Eggs that don’t hatch after 72 hours are most likely unfertilized and should be removed. As time pass, these eggs will develop fungus and rot. Then, they will produce ammonia and ruin the water chemistry.

In most cases, the bettas themselves will eat the unfertilized eggs. However, sometimes there are just too many for them to consume. This is where you should step in and remove them manually.

References

https://www.researchgate.net/figure/Main-stages-of-the-embryonic-development-of-Betta-splendens-A-Egg-cell-B-0-2-h_fig1_258525240