How Long Are Swordtail Pregnant For?

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I know a common joke about Swordtail fish. And that is, a Swordtail fish is not pregnant only when it is pregnant! Besides the joke, you should know that Swordtail fish get pregnant much quicker and frequently than any other species of fish you know.

Swordtail fish are pregnant for an average duration of 28 days. But, the pregnancy can be as short as 25 days to as long as 35 days. The delivery of fry can delay due to stress, bad water parameters, etc. Swordtail can store sperm in their belly for many months so they can get pregnant every other month. Sometimes, though, Swordtail fish seem to be pregnant but it’s just fat depositing on their belly.

If you are wondering whether your Swordtail is pregnant or not, she mostly might be. But, I ask you to read the following before coming to that serious conclusion.

Interesting Facts Regarding Pregnant Swordtail

The swordfish you know is quite a special breed; Special enough to be gifted with a sword. Only males have the sword though. Females are devoid of that special sword, sadly.

You might hear that even the female Swordtail turns into a male. But, the fish might be a late bloomer who develops the sword only later in life.

Anyway, let me not spill more beans and let you read some interesting pregnancy facts.

Duration Of Pregnant Swordtail

Swordfish remain pregnant for roughly 28 days. But, this duration may vary due to stress, water condition, health, and other factors.


Unlike other fish who lay eggs, your Swordfish lays baby Swordfish directly as a whole. No, your Swordfish doesn’t lay eggs.

Swordtails Are Always Pregnant

You might be shocked at how constant your Swordtail remains pregnant. Swordtails are pregnant as soon as they develop the capacity. 

Moreover, you might notice your Swordfish always getting pregnant even after separating from males. Interestingly, female Swordfish can store sperms. So, multiple inseminations are possible.

You might overpopulate Swordfish in your tank in the blink of an eye. So, be careful.

Breed With Other Species

Swordfish can breed with guppies and Platy fish too. Talk about inter-breed infidelity!

How Will You Prevent Swordtail From Being Pregnant?

You will be excited to see the first batch of a Swordtail fry but later on, it becomes monotonous. Owing to how common Swordtail fry becomes, you might want your female Swordtail to stop breeding.

Moreover, you might not have the budget to raise so many Swordfish fry.

So, you can control their breeding in the following ways.

Separate Male From Female

You can easily distinguish males from females. Males have a sword for breeding and females lack the sword.

You can get two tanks. Then, keep the males in a separate tank from the females.

Since Swordtail is peaceful fish, no aggression occurs while separating.

Place Some Plants

You can notice males harassing the female Swordtail in the tank. It is usually prominent during breeding time.

To reduce this harassment, you can provide plenty of plants in your tank. Then, your female swordfish can hide in the plants and protect herself from the males.

How To Determine If Swordtail Fish Is Pregnant?

Even after trying everything in your means, your Swordtail fish might become pregnant. Or is she?

Well, below are some clear-cut signs to know if your Swordtail is pregnant.

Contact With Male 

If your female swordfish was Or is in the same aquarium as a male swordtail, there might be a high chance your swordtail is pregnant.

Also, the female can store sperm in their body. A female can give birth every 28 days up to 6 months even in absence of a male. Thus, even without contact with males, female swordtails get pregnant.

Bulging Belly Of Pregnant Swordtail

The first telltale sign of a pregnant Swordfish is a swelling belly. Initially, the swelling is small which gradually becomes larger with time.

Gravid Spot

If your swordfish has a black spot near the anal fin, she might be pregnant. That spot is called a gravid spot. This is usually your fish’s uterus pressing her abdominal wall.

The darker the gravid spot, the further along in pregnancy is the female Swordtail.

Eyes Of Fry

After some days, the eyes of the fry may be visible through the gravid spot.

Square Belly

At the end of pregnancy, the belly becomes squared in shape. This is opposed to the usual belief that a pregnant belly is rounded.

Secluded Place

At the end of pregnancy, female Swordtails hide in a safe spot. Those safe spots are behind plants, decorations, etc.

She is trying to save her fries who might be eaten by predators in your tank.

So, if your Swordfish swims at a low level and hides, she might be pregnant.

Causes Of Delayed Birth In Pregnant Swordtail

33 days have passed. Yet, your Swordtail isn’t giving birth to any fry.

You might wonder if she is really pregnant. Maybe your fish has an infection called dropsy (swollen belly)?

But, you have seen the gravid spot, eye of the fry, and a square belly; the surest sign of pregnancy. Yet she hasn’t birthed fry on the expected date of delivery. You are dead worried.

Fret not! There are some reasons why your Swordtail isn’t giving birth even though she is pregnant.


Too much stress changes the hormonal pattern in your fish. As a result, there is delayed childbirth.

Moreover, you should avoid changing tanks often. Also, try not to seclude your Swordtail for a long time in the breeding tank.

Unfavorable Water Parameters

The water temperature, quality, pH, DH, size, should be maintained for proper birth. Otherwise, your Swordtail might feel uncomfortable birthing babies.

Ideally, temperatures of 65-80 Fahrenheit, pH of 7-8.3, and DH of 12-18 are suitable for pregnant Swordtail.

Maybe Your Swordtail Isn’t Pregnant

You might mistake the hue of the uterus with the gravid uterus. This hue is present in all the female swordtails. 


Why Don’t Female Swordtail Have Sword?

The elongated sword in the male Swordtail is gonopodium. This sexual dimorphism separates males from females. Females lack this sword. 

Maybe this sword was a call made by nature to separate the male swordfish from the female. 

What Is The Lifespan Of Swordtail Fish?

With Proper care, Swordtail fish can live up to 6 years. 


I hope you got the answer to how long your Swordtail remains pregnant. Although the average duration is 28 days, the pregnancy can vary due to stress, health, water condition, etc. 

If you give proper care to your Swordfish, she will give birth at the right time. So, you don’t have to worry.