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What Do Betta Fish Eggs Look Like?: Detailed Images & Care Guide

What do betta fish eggs look like? Well, firstly they’re very small! But you can tell unfertilized from fertilized, and healthy from unhealthy eggs if you know what to look for…

By Matt Thomas
Last updated on

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what do betta fish eggs look like

Breeding your betta fish can be an amazingly rewarding experience. But one of the key questions during mating is what do betta fish eggs look like?

Betta fish eggs are tiny, at around just 1mm in diameter. They are often oval in shape and are white when unfertilized, changing to a light yellow once fertilized.

But during my time breeding bettas, and subsequent research, I’ve found other tiny differences depending on the egg’s stage of development. And there are even differences that can help you tell healthy from unhealthy eggs.

So keep reading if you want to understand these differences in detail, along with how mating occurs in your betta fish, how many eggs to expect and hatching times, and even how best to care for them!

What Do Betta Fish Eggs Look Like?

Your betta fish eggs can look slightly different depending on whether they are unfertilized, or fertilized and what stage of development they’re at. Just remember betta fish eggs are pretty tiny, so you’ll need to look very closely to see the changes!

What Do Unfertilized Betta Fish Eggs Look Like?

Unfertilized betta fish eggs are small, often at around 0.9 to 1 mm in domestic Betta splendens [1], but it is possible for you to see them in the water when your female betta fish spawns.

unfertilized betta fish eggs
Close-up showing unfertilized eggs of Betta splendens

They appear quite white in color and slightly more translucent than once they have been fertilized. And unlike fertilized eggs, they’ll have no gray dots or areas that indicate the presence of an embryo.

You’ll also notice the shape of your betta fish eggs can vary too. In many cases, they can be oval rather than a perfectly round sphere.

What Do Betta Fish Eggs Look Like During Developmental Stages

Once your betta fish eggs are fertilized, they’ll start to show tiny differences as the embryo develops into a betta larva. 

Again bear in mind, as the eggs tend to get no larger than 1.5 mm while developing, these changes can sometimes be very difficult for you to see with the naked eye.

  • Fertilization: During mating, your female betta will release her eggs into the water while the male releases his sperm or ‘milt’, which quickly fertilizes the eggs [2]. Milt appears as a very thin white cloud so you may struggle to see it in your tank.
  • Early Embryonic Development: The newly fertilized eggs are white or a very light yellow in color [3]. After around 3 hours you may start to see one or two very tiny gray spots appear as the embryo starts to develop [4].
  • Late Embryonic Development: Prior to hatching, the embryo will have developed into a fully formed larva with a tiny tail. Features like this are very difficult to see though as the larva is still likely to be less than 1 mm in length at this stage [5].

What Do Fertilized Betta Fish Eggs Look Like?

Fertilized betta fish eggs will initially remain white in color, although may turn to very light yellow after around 3 hours. The gray spot of the blastula (or early embryo) should also appear around this time [6].

fertilized betta fish eggs showing developing embryo
Magnified image of fertilized eggs of B. splendens with embryo circled

As development continues, the fertilized betta fish eggs may start to become a slightly darker yellow. But again it can be difficult to clearly see the change, especially when the eggs are being incubated in your betta’s bubble nest amongst all the bubbles.

What Do Infected Betta Fish Eggs Look Like?

Once your betta fish eggs hatch you’ll hopefully have a new brood of betta fry which will go on to develop into healthy juveniles. But it’s also very likely you’ll have a number of eggs that either weren’t viable and didn’t hatch, or weren’t fertilized in the first place.

If you leave these eggs in your tank they can eventually become infected by water molds. One of the most common of these fungal infections is Saprolegnia spp., which can also cause diseases like body fungus on your betta fish.

fungi infected betta eggs
Eggs of B. splendens showing early onset of fungal infection

Unfertilized or unviable betta fish eggs that have been infected by fungi can appear more translucent than the yellow color of fertilized eggs. But you’ll also see a cotton-like white mass appear around infected eggs which is quite easy to spot [7].

Fungal infections can easily spread to fertilized eggs but if you keep a clean tank it’s very unlikely you’ll see water mold appear before the rest of your betta fish eggs have hatched.

Betta Fish Breeding Behavior

Courtship and mating in betta fish are quite involved and can take your bettas several hours. We could go into plenty of detail here but instead let’s focus on the highlights, particularly in relation to the care of betta fish eggs.

Male Betta Behavior During Breeding

If you’ve previously kept a betta fish you’ll know that males, in particular, can be aggressive and you should only keep one male in a tank. But males can also be aggressive towards females, so only keep them together for short periods when breeding.

You also need to take care when introducing your breeding pair together. Before your male and female are ready to mate they will often engage in chasing and what looks like mild fighting which can last around 2 to 4 hours.

Do keep an eye on this courtship and if the male shows particular continued aggression, such as constant biting, be ready to separate them as they may not be ready to start breeding. You can use separate tanks, or an easier alternative is to use a tank divider to section off the male.

Why Betta Fish Build Bubble Nests

Once courtship has started, you should see your male betta start to build his bubble nest as it’s he who will care for the eggs and fry once they hatch. He produces mucus from his pharyngeal organ to build the bubble nest [8]. 

The bubble nest holds the eggs near the surface of the water, keeping them well oxygenated while protecting them from temperature changes. Wild bettas evolved this trait as it allows them to rear young in shallower areas with lower oxygen levels where they can avoid predators [9].

Betta Mating And Egg Fertilization

Just prior to mating, your male may continue to chase the female to engage her in their courtship dance. This can look aggressive and they may both flare repeatedly, but when ready they will curl around each other.

During this embrace, your female will release her eggs as the male releases his milt. This can happen several times for around 3 hours [10]. But once complete, remove the female from your tank as your male betta may start to become aggressive towards her again.

It’s also important you remove the female as she may eat her own fertilized eggs [11]. In contrast, male bettas often eat unviable or unfertilized eggs to support the nest overall. But they sometimes eat fertilized eggs if stressed, so do try to keep them in a quiet, calm environment.

Incubation Behavior In Betta Mouthbrooders

While bubble nest building betta fish like Betta splendens are most common in home aquariums, there are other bettas such as Betta macrostoma and Betta simplex that are mouthbrooders [12].

Instead of building bubble nests, mouthbrooding bettas incubate their eggs in their mouths before hatching. At around 2 to 3 mm, the eggs of mouthbrooding betta fish tend to be larger than bubble nest builders and they also produce bigger offspring [13].

Mouthbrooding bettas evolved this way of incubating their eggs to protect them from predators and other threats. Not only does it allow the male betta to closely guard their eggs, but unlike bubble nest builders, they can move wherever they need to avoid danger [14].

Some studies also suggest mouthbrooding bettas adapted this way of caring for their eggs as they live in areas with stronger currents which would make bubble nests too difficult to build. Although other studies have found them in similar places as bubble nest builders [15].

male and female betta fish embracing

How Many Eggs Will My Betta Fish Lay?

The number of eggs your betta fish will lay in a mating session can vary greatly, which is why you may see different answers to this question online. 

In fact, Betta Splendens can lay from 10 to just under 500 eggs in one mating session in some cases [16, 17, 18]. The average clutch size can be around 250 to 350 eggs though [19, 20]. But remember, not all of these eggs will be fertilized during mating and go on to become fry. 

There are several factors that can influence the number of eggs your betta fish produces.

Species And Inbreeding

The species of betta fish can greatly influence the number of eggs produced. Mouthbrooding betta fish for example lay a lot less than Betta Splendens, at around 20 eggs per mating. This is not surprising given their young are larger and hatch in their mouths rather than in a nest [21].

Betta fish that have been inbred may also lay fewer eggs [22]. Inbreeding between betta fish can affect their health in many ways, including how many eggs the female can produce.

Betta Fish Health And Conditioning

Female betta fish use more energy during egg production and breeding than they normally would. You can support this energy need by ‘conditioning’ your betta starting around 2 weeks before breeding.

Conditioning is where you feed your betta high-protein animal foods at least 3 to 4 times a day. This can include frozen and live foods like bloodworms, brine shrimp, or tubifex. High-protein animal foods help provide the energy needed to produce a larger brood [23, 24].

Male bettas also benefit from this conditioning as these high-protein animal foods are a great source of carotenoids. These help your male enhance his color and increase his redness, making him more attractive to the female [25].

Size And Age Of Your Female Betta

While female betta fish can reach sexual maturity at around 110 days old, or 3.5 months [26], they don’t become fully grown until around 6 months. In fact, the best time for you to start breeding your betta fish is around 8 to 12 months when they’ve had time to mature.

Female betta fish younger than 8 months are smaller and generally don’t have the same energy reserves needed for increased egg production as older fish. However, if you wait too long your betta can become less fertile. This generally happens at around 3 years old.

Spawning Experience Of Your Betta

The spawning and breeding experience your betta has can also affect the number of eggs she produces. Studies have shown that experienced female bettas lay more eggs than those with little or no experience [27].

Not only this, but experienced pairs of male and female betta fish tend to fertilize more eggs during breeding. And experienced males even tend to be better at retrieving more of the fertilized eggs and moving them safely to their bubble nest [28].

How Long Before My Betta Fish Eggs Hatch?

Typically, betta fish eggs can hatch anywhere from 2 to 3 days after fertilization. However, there are several factors that can affect how quickly your betta fish eggs will hatch. Let’s take a look at them below.

The Species Of Betta Fish

In Betta splendens, the typical hatching time of your betta fish eggs should be between 2 to 3 days but can be as little as 24 hours. This can be much longer in mouthbrooding species such as Betta simplex though. 

While mouthbrooding is a good way for the betta to protect its eggs, it tends to take longer and the resulting fry are larger once they hatch. The process of hatching in mouthbrooders can take from 2 weeks to a month [29].

Water Quality Of Your Aquarium

Just as the water quality of your betta fish tank can affect your betta fish, it can also impact the hatching of your betta’s eggs. If your tank is not properly maintained, fish waste and uneaten food can lead to a build-up of ammonia which is very harmful to both your eggs and fry [30].

If you notice many of your betta’s eggs fall to the bottom of your tank this could be a sign they have become unviable due to ammonia. To prevent this, make sure you have the right filter for your tank installed and perform your tank maintenance at least weekly.

Your Tank’s Water Temperature

Wild betta fish originate from areas of South East Asia including Thailand where temperatures can be up to 85°F in the breeding season [31]. But in reality, this is a little too high for your home aquarium as it can lead to your eggs hatching before they are fully developed.

Further studies in domestic betta fish have shown that a temperature of around 79.8°F is best both for bettas to build their bubble nest and for egg development [32]. This temperature can also help your female betta when spawning as well as reduce the hatching time of the eggs [33].

Oxygen Level In Your Water

The oxygen level in your water can also affect how quickly your betta fish eggs hatch as a high oxygen level helps the embryos develop faster. And as mentioned earlier, this is a key part of why male betta fish build their bubble nests at the surface [34].

Your filter not only removes waste from your tank but is also great for oxygenating the water. If you want to further increase aeration you can add an airstone too. Just ensure your filter and pump are adjustable as a strong current will stress your fish and their fry [35].

betta fish with bubble nest

How Do I Care For My Betta Fish Eggs?

Whilst your male betta fish will be very attentive to his eggs while they develop and hatch, there are a few things you can do before and after mating takes place to give your betta fish eggs the best chance of hatching into healthy fry.

Keeping Males And Females In Separate Tanks

As mentioned previously, male bettas are not only aggressive towards each other but they can also show aggression towards females. Keeping your male together with your female for several days can cause her significant stress.

For this reason, keep your male and female separated until you are ready to introduce them into your breeding tank. And when you do introduce them, use a tank divider to keep them separated while they get used to their surroundings and each other prior to mating.

What To Do Once Your Betta Lays Her Eggs

Once your female has laid all of her eggs during mating, usually within about 3 hours, remove her from the breeding tank. This will allow the male to transfer the eggs into the bubble nest and begin to care for them without the threat of her eating them.

Monitor and maintain the water temperature at around 79.8°F, and make sure that the tank stays clean. As well as cleaning any obvious gunk out of your filter, this may also mean carefully vacuuming the bottom of your tank if you get a build-up of excess leftover food.

What If My Betta Fish Eggs Don’t Hatch?

All of the betta fish eggs that have been fertilized and are viable should have hatched within 3 days following mating. Any eggs left after this time may have been infertile or unviable. And as previously mentioned, you are likely to be left with many unfertilized eggs too.

Once these 3 days have passed and you have a tank of healthy fry, you should remove the remaining eggs. This will make sure they don’t start to decompose or become infected with water molds which can be harmful to your newborn fry.

What To Do Next?

While betta fish eggs are tiny, once you know what to look for it is possible for you to tell the difference between unfertilized and fertilized eggs, and also if they have become infected.

Knowing what betta fish eggs look like can help you give them and your betta fish the best possible care as they hatch into fry.

And once you do have a tank of healthy juveniles why not find out all you need to know to give them the best betta fish care by reading our guide too!

Frequently Asked Questions

Take a look at the answers to some of the most frequently asked questions when it comes to betta fish eggs and what betta fish eggs look like!

Can Betta Fish Produce Eggs Without A Male?

Female bettas can produce eggs without a male but they’ll usually re-absorb them. If released these unfertilized eggs won’t develop, and instead will likely become infected with fungi.

How Do I Know When My Bettas Are Ready To Mate?

The colors of both your male and female betta fish will darken when they are ready to mate. You may also notice the female’s ovipositor, where her eggs are produced, become more visible.

How Can I Tell If My Betta Fish Eggs Are Fertilized?

Fertilized betta fish eggs will turn from white to light yellow. They may also grow slightly from about 1mm to 1.5mm, and you may notice a gray spot where the embryo starts to form.

How Often Do Betta Fish Lay Eggs?

Once your betta fish has laid her eggs she’ll need about 2 weeks before she can produce another clutch. Although in reality, most bettas will only lay eggs once or twice a year.

*Some images are for illustrative purposes.

Photo of author
Matt Thomas
Matt has been keeping fish since junior high when he used to look after his parent's tank. He loves guppies, cichlids, and his crowntail betta named Bobby.

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