How Long Are Swordtail Fish Pregnant For?

Lauren Kiekbusch
How Long are Swordtail Fish Pregnant For

When female live-bearing fish get pregnant, their stomachs swell, and when their tummies get particularly huge, it means they’re about to give birth. Unfortunately, we can’t always predict when they’ll do so or how they got pregnant in the first place.

Female livebearers are frequently pregnant when purchased since they are housed together with males at aquatic stores and supply companies.

The gestation period of the swordtail fish varies greatly depending on the age and size of the fish and water conditions, diet, and stress levels. Livebearers, like mammals, can give birth prematurely and only have a few fries at a time.

In general, as they grow larger, they discharge a more significant number of fry each time. In this article, we are going to discuss the period in which the swordtail fish get pregnant.

Also worth reading;

  1. Swordtail Fish Fry Care – How to Care for Baby Swordtails?
  2. Why Do Swordtail Fish Eat Their Fry? (All You Need to Know )
  3. Do Swordtail Fish Sleep?- You Might Be Interested To Know

How Long Are Swordtail Fish Pregnant For?

Swordtails have a gestation period of 28 days. However, delivery can delay due to poor water conditions, stress, or other circumstances.

So, shortly before the gestation period, I would advocate removing the female from the others. You can be sure that the majority of the swordtail fry will be safe this way.

Female swordtails are already under a lot of strain when it comes to giving birth. To avoid further stress, attempt to keep the female in the same water conditions as previously.

The water temperature should be between 70 and 82 degrees Fahrenheit (21-28 degrees Celsius). The pH of the water is set around 7.0 to 8.3, and the water should be between 12 and 18 DH.

Because swordtails are highly social fish, it’s best not to keep the pregnant female separated from the others for too long. Put her back in the main tank after giving birth and wait for the fry to acquire strength and begin swimming.

If you’re interested in breeding and growing swordtails, I’ve written a comprehensive guide on swordtail fish fry care that you should read.

Determining A Pregnant Swordtail Fish

If a swordtail is pregnant, you will notice that their tummy grows more extensive, but you should also look for other signals that they are ready to give birth.

When a female is on the verge of giving birth, she will distance herself from others and become more aggressive with males. It will also hide in a corner, restricting its movement to that area.

Swordtails are more likely to become pregnant. That is why most people would tell you that all you have to do is fill the aquarium tank with water. Although this is an exaggeration, keeping females and males in the same tank involves caring for new swordtail fry several times a year.

A swordtail fish will become pregnant very shortly after giving birth, and it will take advantage of this predisposition.

You may have the impression that your swordtail is constantly pregnant, and as a result, you have forgotten how non-pregnant swordtails appear.

Each new fry will mature in a short period, allowing them to contribute to the population of your aquarium – this will take about three months. A few swordtails can overpopulate your aquarium tank if you aren’t careful.

How To Prevent The Swordtail Fish From Getting Pregnant

New fry every few days is one of the things I enjoy seeing. It brings me great joy. However, due to a variety of constraints, I must implement several control mechanisms.

Allowing a swordtail to breed quickly is difficult, especially when my tank is small and my budget is restricted. As a result, I prefer to keep my swordtail females in separate aquarium tanks to avoid unintended pregnancies.

When the time comes to breed them, males are usually easier to bring to the tank because they are smaller. Swordtails are calm creatures, and segregation does not make them aggressive or stressed. When a female swordtail is present, the males appear to be more aggressive, and inexperienced.

It is because they harass females to mate with them more frequently. If you don’t want to spend the money on two different tanks, you can buy a male swordtail and sell it after impregnating the females.

Causes Of Delayed Birth In The Swordtail Fish

A swordtail’s gestation period is 28 days, but the delivery usually takes two or three days longer. If this happens frequently, especially for more than a month, you should be aware that something is wrong and that you must change the aquarium tank.

The problem is frequently caused by poor water conditions or a tank that isn’t large enough for the fish. According to veterinarians and store owners, swordtail fish should be kept in a 20-gallon aquarium tank with heavy planting.

They also instructed me to maintain a water temperature of 64-83 degrees Fahrenheit, a PH of 7.0 to 8.3, and a water hardness of 12 to 18 DH.

Stress can also cause pregnant swordtails to be late in delivering their young. Transferring the swordtail from one tank to the other more frequently or isolating the swordtail from the others is one of the leading sources of stress.

If adjusting the water conditions and reducing stress haven’t yielded any effects, the swordtail is most likely not pregnant. Many believe that the gravid patches on pregnant swordtails are fry’s eyeballs. That is a misunderstanding. It could be the uterine color, which is present in all swordtails.

You Might Be Interested to Know: Do Swordtail Fish Sleep?

What Is The Maximum Number Of Times A Swordtail Fish Reproduces?

A swordtail will begin breeding once it reaches three months; thus, it’s best to separate them by sex before reaching that age. Your swordtails, such as hardness, PH, ammonia, nitrites, and nitrates, will often spawn if the water conditions are ideal.

The stress level will be minimal, and spawning will be high if the water condition is within the appropriate ranges. After the first birth, a swordtail can reproduce 4-6 times.

Experts say the second birth session can take up to six months and can happen any time after the girls and males have been separated. Swordtails can store sperm for up to eight months and use them for fertilization.

Because the fish can consume their young, you should adequately feed them as they approach the time of birth. You should also remove the fry from the main tank once they are born to protect them from the ravenous fish.

Swordtail fry is about the size of a pen’s point, and they’re as transparent as bubbles. When purchasing your fish, inspecting the fry to determine when the fish has given birth is always good.

Adding more living plants into the aquarium tank to give them appropriate hiding places is the other approach to sheltering the swordtail fry. Stones and driftwood can also be used as hiding spots.


Separating the fish based on their gender may seem like a good idea, but swordtails will always surprise you. Some individuals claim they will turn into males if they keep their female swordtails alone in a separate tank.

However, according to the experts, those are late-growing males with swordtails who develop their male genitals late in life. Swordtails do procreate in the absence of males, as legend has it.

Females can store sperm for up to eight months and conceive numerous times following single insemination. Another fascinating fact about swordtail fish is that they can breed with platies because they are both members of the same family.

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