How to Tell if Swordtail Fish is Pregnant?

How to Tell if Swordtail Fish is Pregnant?

Swordtail fish are prolific breeders that can get pregnant every month which means if your female swordtail fish is bloated, she’s almost certainly pregnant. So, how can you tell when the female swordtail is pregnant?

As the pregnant female swordtail fish contains fertilized eggs inside her tummy, she will be fat. The newborns are all developed within her causing her to bloat up like a balloon. If you observe her closely, you’ll see that her once slim body is now round and bulbous.

In this article, we’ll give you some tips on how to tell if your swordtail fish is pregnant and how to care for it.

Check If the Fish Is Female

To begin, you must determine the gender of your swordtail fish by looking at their caudal fins.

The male swordtail has a slender, sword-like extension that protrudes from the tail. The sexes of swordtail fish may be determined in this manner with absolute confidence.

This is necessary because only female swordtail fish can get pregnant. Therefore, once you have realized that your swordtail fish is a female, there is a high probability that her fatness is due to her pregnancy!

See If Your Swordtail Fish Mate

During mating, the male swordtail will try to chase the female swordtail. Then it will extend his pointed gonopodium and inseminate the female swordtail fish. This action is, without a doubt, fast.

The males of a mixed swordtail tank will quickly fertilize the female swordtail fish. As a result, there’s a good chance your fish is pregnant rather than just overweight.

Check the Female Physical and Behavioral Changes

a. Physical Changes

1. Growing Belly

This is a sign commonly observed in all species of animals, including fish. The female will not show any outward symptoms at first, but things will become more apparent 2 weeks into the pregnancy.

The abdomen will visibly expand as the delivery moment approaches, often at an accelerated rate.

If you’ve ruled out overfeeding and sickness as possible reasons for your physical transformation, pregnancy is the only other explanation.

The female’s belly will start to look more square by the 28th day of the pregnancy. That is a sign that labor is just around the corner.

2. Gravid Spot

The gravid spot is a dim area of the fish’s abdomen that may be viewed from both sides of the body.

Swordtails are livebearers and have their eggs hatch inside their bodies. As a result, they will give birth to live fry.

At that point, the fry will grow and take up more space, making the gravid spot darker and larger. This happens because the fry’s eyes are all crammed in the same location, which is why it looks so black.

b.Behavioral Changes

1. Increased Appetite

Swordtails eat one or two times per day, depending on how many of them you have.

They aren’t often big eaters, but pregnant females alter that. They will eat more food, more frequently, and fight for it.

If you’ve already confirmed that your swordtail is pregnant, expect to have to feed it more than usual.

After all, it’ll need the additional calories and nutrition to support its growing pregnancy and nurture the fry.

2. Hiding from Males

When it comes to their mating rights, males are always aggressive. They are unconcerned whether the females have previously mated and are no longer interested in their service and they’ll keep advertising themselves by following the female around the tank, poking it, and hoping for a lucky strike.

If you notice that your female swordtail is constantly being chased by males around the tank and tends to hide, she might be pregnant.

But you must be cautious because when the male starts acting aggressive and territorial, it may intimidate or stress out the female and cause her to hide.

Stress can lead to a variety of health issues, including a weakened immune system and even early delivery, this is not a good setting for your pregnant swordtail.

In this case, if the males’ persistence doesn’t wear off, you may want to relocate the female into a different habitat, preferably alone, until the pregnancy reaches term.

3. Aggression

Swordtails are usually calm fish. They only become violent when it is necessary, for example when they are defending their territory or a specific social hierarchy.

However, that changes a little during pregnancy, pregnant females will be irritable and snap at anyone nearby.

They won’t necessarily resort to excessive violence, but you should be able to observe a lot of poking and chasing.

Not all females will behave in the same way or with the same intensity, but if a female becomes over-aggressive, you should consider separating her from the others.

How to Care for Your Pregnant Swordtail Fish?

Swordtail fish during pregnancy require particular attention to guarantee a successful gestation and delivery of healthy fry.

Here are some simple things you may do to ensure your fish has a successful pregnancy:

1. Prepare Separate Breeding Tank

We suggest that you invest in a separate gestation tank, especially during the final stages of your swordtail’s pregnancy. Trust me, your fish will appreciate it.

A separate tank has benefits like:

  • The male Swordtail will not bother a pregnant Swordtail.
  • You will not have to worry about your pregnant swordtail experiencing tension during birthing.
  • Adult Swordtails have been observed to consume newly hatched fry. This may be prevented by using a separate tank.
  • After reproducing, the mother Swordtail will have time to relax.

Another option is a tank divider which will do the job. However, it is preferable to purchase a separate tank for your pregnant Swordtail.

2. Proper Nutrition

As mentioned before, pregnant females need more food than their non-pregnant counterparts. They require extra calories and nutrients to support the pregnancy and to help the baby grow.

To make sure your fish receive all of the nutrients it requires, feeds it a high-quality diet that includes live, frozen, or freeze-dried foods.

A plus to that, bloodworms, brine shrimp, daphnia, and krill are all good options. Spirulina or other vegetable-based foods can also be added to their diet.

3. Ample Swimming Space

Pregnant swordtails need plenty of room to swim and explore. A small tank will only stress them out and make it difficult for them to find food.

As a result, you may need to aim for a tank that’s at least 20 gallons for a single fish and 30 gallons for a pair.

4. Stable Water Conditions

Water quality is important for all fish, but it’s especially crucial for pregnant females. Poor water quality can lead to a variety of health problems, including miscarriages, birth defects, and premature births.

You should adjust the water parameters as follows:

  • A Temperature of 74-80 degrees Fahrenheit
  • pH between 7.0 – 8.4
  • 10% water should be changed every week. 25% water changed every 2 weeks.

To ensure that your fish has stable water conditions, test the water frequently and make changes as needed.

5. Add Hiding Places

Although you’ve moved your pregnant Swordtail to a separate tank, she may still be stressed and unable to give birth.

If your aquarium is experiencing this problem, consider adding some aquatic plants and some hiding places.

Normally, pregnant Swordtails hide their young behind plants so that they are well sheltered. She’ll feel as though she’s back in the wild once more.

6. A Quiet Environment

Pregnant swordtails need a quiet environment to feel safe and secure. A loud, chaotic tank will only stress them out and make it difficult for them to rest and heal.

To create a peaceful environment, keep the tank out of direct sunlight and away from loud noise.


How Long are Swordtails Pregnant?

Swordtail pregnancy lasts about 28 days on average. In certain circumstances, it may last longer, but not by much.

As a rule of thumb, if the pregnancy lasts longer than a month, there is something wrong.

How Many Fry Can You Expect From a Swordtail?

Swordtails, like other livebearers, can produce 5 to 80 young at a time. The typical number is 30-35.

A swordtail can produce babies each month if there is a male in the tank and if the female is maintained and fed correctly.

Last Words

Pregnant swordtails are a bit more high-maintenance than your average fish, but they’re still relatively easy to care for.

First and foremost, pregnant fish need good water quality and stable water conditions. They also need plenty of room to swim and plenty of places to hide.

Finally, make sure the tank is quiet and peaceful to not stress out the fish.

If you take these precautions, your pregnant swordtail fish will have a much better chance of giving birth successfully.

We hope you learned something from this article. If you have any questions or comments, please feel free to leave them below. Thanks for reading!

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