How Do Zebra Danios Breed?

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All Danios are egg scatterers. But the Zebra Danio is probably the easiest egg scattering fish to breed in the home aquarium. So as long as you have both males and females in your tank you’re likely to find that the population increases.

Because the Zebra Danio (aka Zebrafish) is an egg scattering fish it means that the eggs are fertilized externally. The female scatters her eggs and as she is scattering them the male releases his milt (semen) onto them. The eggs continue to fall to the bottom of the tank and may also land on plants and tank decorations. The fertilized eggs then develop and hatch into Zebra Danio fry.

Even in an aquarium environment Zebra Danios will breed prolifically. And that goes for most other varieties of Danios too. Whether you’re actively planning to breed them, or you’re just happy to wait and see what happens, knowing what to look out for is a great help.

So let’s take a look at how Zebra Danios breed and how to protect the fry (babies)

How Can I Tell If My Zebra Danio Is Male Or Female?

The first thing you need to know when it comes to breeding Zebra Danios is whether you’ve got both males and females in your tank. I know that this sounds like and obvious statement but sexing Zebra Danios isn’t simple.

Telling the difference between male and female Zebra Danios isn’t always easy. In fact it can be quite difficult.

However, there a few generally accepted pointers for telling males from females.

• Males are slimmer and more torpedo shaped than females
• Males are usually a bit smaller than females
• Males often have a more golden tint between the stripes and also along their back bone
• Females have a more rounded belly than males so they have room to carry eggs

The differences between male and female Zebra Danios are subtle so it can be really hard to tell them apart. Although it can become a little easier the longer you keep these fish because you’re more likely to spot the differences between the two over time.

The best solution to getting both sexes at the start is to ask for a mix of both males and females when you buy them. But don’t be surprised if even your Pet Store or Aquatic Dealer get it wrong despite their best efforts. It really is that difficult to determine their sex, particularly when they’re young.

Another way to increase your chances of getting both male and female Zebra Danios is to keep them in a decent sized group. Because Danios are a schooling fish they prefer to live in groups of at least 5 anyway. The more you keep together the happier they will be and the greater the chance you’ll have of them breeding.

How Will I Know That My Female Zebra Danio Is Ready To Breed?

When a female Zebra Danio is ready to breed her belly will swell. So you’re going to notice that she looks fatter than usual. And unless you’ve been overfeeding your tank it’s a good indication that your female Zebra Danio is in breeding mode.

Her swollen belly is due to the eggs she is carrying ready for their release during mating (spawning). And because Zebra Danios are egg scatterers the eggs are unfertilized at this point. Which means that you can’t describe the female as being pregnant. Nonetheless, she is ready to reproduce young.

What Does Zebra Danio Breeding Behaviour Look Like?

Once your female Zebra Danio is plump with eggs and ready to breed you will notice a change in the behaviour of the males. Although always a lively little fish anyway the males will now become super energetic in their efforts to breed with the female. And because Zebra Danios pair for life it’s important for a male to be the one chosen.

The males will energetically chase the female(s) until one male and one female become a mating pair. This can take a couple of days or so. Once the paring had been established the serious business of spawning begins.

Zebra Danio Spawning Behaviour

Spawning is the time when the female Zebra Danio releases her eggs and the male fertilizes them as they fall through the water. The male encourages the female to release her eggs by swimming around and alongside her, often touching her with his body. Their movements are fast, almost frantic, while this spawning activity is playing out.

Every time the female releases some of her eggs the male Zebra Danio releases his sperm into the water to fertilize them. This process can go on for some time until all of the eggs are released.

Because spawning usually happens at first light, or in the early hours of the morning, it can be difficult to get the chance to see it happening. So unless you’re an ‘early bird’ you might not even know that it’s happened.

I came across this YouTube video of Zebra Danios spawning. It’s a short video showing a single pair of Zebra Danios spawning in a breeder box. The video is by Tessa Montague and clearly shows how fast and frantic the spawning process is.

https://www.youtube.com/watch?v=oRf4JHbTJgM

What Do Zebra Danio Eggs Look Like?

Zebra Danio eggs look like minute pearls and are generally just under a millimetre in diameter. They are visible to the naked eye if you know what to look for. Whether you will be able to see them or not will depend on where the eggs land. Zebra Danio eggs can be difficult, if not impossible, to spot amongst the plants and substrate of an aquarium. So don’t be too surprised if the first thing you notice after your Zebra Danios have spawned is the tiny fry swimming around the tank looking for food.

How Many Eggs Do Zebra Danios Scatter/Lay At A Time?

Zebra Danios can scatter/lay 100 plus eggs during each breeding session. So if you have several breeding pairs in your tank they are likely to produce several hundred eggs over a short period of time. And on a regular basis too. A successful breeding pair can spawn on an almost weekly basis. But the frequency can vary depending on the individual pair.

How Long Does It Take For Zebra Danio Eggs To Hatch?

As a general rule it takes about 2 days for Zebra Danio eggs to hatch. When they have hatched these tiny fish are only about 2 millimetres long and are called wrigglers. The reason for this name is because that when Zebra Danio fry hatch they wriggle rather than swim. During their time as wrigglers they feed off their yolk sac. Once they get to about 2 days old they become free-swimming and are then called fry. This is when they set off in their search for food.

When Zebra Danio Fry are swimming freely in the aquarium they are easier to see. Which means you’ll have a better idea of how many new fish you have in the tank. And also how much extra food you will need to put into the tank.

All food for Zebra Danio fry needs to be small enough for them to eat. If you would like more information about what to feed your Zebra Danio fry, and also what to feed the adults, take a look at my article ‘What Do Danios Eat?’

Do Zebra Danios Eat Their Own Eggs And Fry?

Zebra Danios do eat their own eggs and fry. In fact a breeding pair will eat the eggs as soon as they are released during spawning. Any eggs that escape being eaten and hatch out into wrigglers will also be eaten if they are caught by the adult fish. The same goes for the tiny free-swimming fry too. So if you want to save as may Zebra Danio eggs/fry as possible there’s a few tips below that will help you to do that.

Tips For Saving Zebra Danio Eggs/Fry

• Set Up A Breeding Tank – The best way to save as many eggs and fry as possible is to set up a separate cycled breeding tank. The tank will need to have a a grid platform at the bottom that allows the eggs to fall through it but won’t let the adults get at the eggs. Fish keepers also use marbles or round pebbles instead of a grid. You also need to keep the water level low above the grid, between 2-3 inches/5.08-7.62 cm. The low water level helps to stop the breeding pair getting the eggs before they fall through the grid. Put your breeding pair into the tank and let them spawn. Once all the eggs have been released remove the adult Zebra Danios and put them back in their original tank. The tank can then be used as a hatchery and nursery until the fry are too big to be eaten.

• Use A Breeder Box – Another way to protect the eggs/fry is to put a breeder box into the main tank. Plastic breeder boxes generally come with a removeable grid platform that let the eggs fall through to the bottom to keep them safe. Once the breeding pair of Zebra Danios have finished spawning you can put them back into their original tank. The breeder box will then act as a hatchery and a nursery. Although you do need to bear in mind that the fry will outgrow the breeder box far quicker than they would a nursery tank. However, breeder boxes are cheap to buy and can also be used to separate an injured/sick fish. They also come in handy as temporary housing for eggs/fry while a separate tank is being cycled.

• Have Densely Planted Areas – Having densely planted areas in your aquarium will give eggs/wrigglers/fry safe places to hide in while they grow. So if you don’t want to set up a breeding/nursery tank, or use a breeder box, plants help to make your main tank as safe as is possible for new arrivals.

• Cover Filter Intakes – Aquarium filter intakes are another danger to Zebra Danio wrigglers/fry. Open gridwork filter intakes and open ended intake tubes can suck in and kill these tiny little fish. So as a precautionary measure it’s best to cover the intakes. How you do this will depend on the type of filter you are running. For example, if you have an open intake filtration tube you can put a pre-filter sponge cover over the end. If you have an internal ‘box type’ filter with a grid inlet you can cover it with a fine mesh (such as ladies tights/pantyhose). If you have a sponge filter run by an air pump you won’t need to do anything because this type of filter is fry-friendly.

If you would like more information about sponge filters read my article ‘What Is An Aquarium Sponge Filter?‘

Other Frequently Asked Questions

How Long Do Zebra Danio Fry Take To Grow?

Zebra Danio wrigglers/fry take about 3-4 months to reach adult size. Although this will depend on the quantity and quality of the food available to them and also the condition of the tank environment.

How Big Do Zebra Danios Get?

The average length of a full size adult Zebra Danio is about 2-2.5 inches/5.08-6.35 cm. It is possible for them to grow to 3 inches/7.62 cm plus, but that is a little unusual for these fish. Although it does happen occasionally.

At What Age Do Zebra Danios Breed?

Although Zebra Danios are considered to be sexually mature at around 3 months old they won’t necessarily start to breed at this age. It’s more usual for them to start to reproduce once they reach between 7-18 months old. And the more mature they are when they start to breed the higher the success rate will be for producing viable fry.

How Long Do Zebra Danios Live For?

When it comes to how long Zebra Danios are likely to live their lifespan is an average of 2-3 years if well cared for. They can live a bit longer depending on diet and tank environment and, of course, depending on each individual fish.

Whether you choose to save the fry, or let nature take its course, enjoy keeping these lively easy-care fish