Why Is My Female Swordtail Being Aggressive

You may be concerned about your female swordtail’s behavior. Swordtail fish are normally gentle and dislike violence. So, if your fish is acting strangely, there’s a chance something is wrong. Thus, if you’re asking why my female swordtail is aggressive, there can be many causes.

Female Swordtail aggression could be due to overcrowding or a lack of food. The most common reason, though, could be that the fish is pregnant and looking to protect herself. Hence, it’s best to isolate the fish until she gives birth. 

In this article, we’ll go over why your female swordtail is hostile and what you can do about it.

Why Does My Female Swordtail Show Aggression?

Swordtail fish are generally calm. Female Swordtails, on the other hand, can be hostile. There are several reasons why this behavior could occur.

The Swordtails may exhibit this tendency if the tank is unclean and crowded. However, the main reason that female Swordtails are hostile is if they’re pregnant.

Swordtails that are pregnant are easily stressed and irritated. Because they carry so much weight, they can only roam in certain areas. When they’re trying to give birth, they shelter themselves among the vegetation in the tank.

As a result, any fish that comes close to the pregnant fish will be pursued and attacked. This is a behavior that is more prevalent during meal times.

It’s best to isolate the aggressive Swordtail fish from the rest of the aquarium for a week or two. If pregnant, you should wait until it gives birth to do so.

Red Swordtail Female

How to Tell if Your Swordtail Is Pregnant?

It can be difficult at times to tell if your Swordtail is pregnant. There are, however, indicators that can be seen that suggest pregnancy.

After three months, a Swordtail will begin reproducing as they reach sexual maturity. You can tell if a fish is pregnant by various appearance changes. Some of these changes include:

  • The bottom of the fish’s belly will start to look somewhat cubic as she draws nearer to delivering a baby
  • A big black blotch will appear around the Swordtail’s bottom upon every side of her torso

When it comes to social behavior, you’ll also observe some changes. Some of these changes include:

  • The fish will isolate itself from others and also become more hostile toward the males
  • The pregnant fish will stay in a spot away from everyone and restrict its mobility inside that zone
  • A decreased appetite and the fish will stop roaming around
  • The Swordtail will remain at the back of the aquarium, where she will rest on the tank’s pebbles. Instead of laying eggs, swordfish give birth to the small fry

A Swordtail’s delivery time ranges between 6 and 12 hours on average.

How to Care For the Pregnant Swordfish?

Caring for the pregnant swordfish is straightforward. In fact, these instructions apply also to non-pregnant aggressive fish.

Isolate the Fish

The pregnant fish should be kept separate from the rest of the tank. Only after your fish has displayed indications of labor, should you remove her from the tank.

Additionally, separate the fry from the mother after the fish gives birth. The fish in the aquarium, even their mother, will perceive the fry to be food. They’ll have to shelter away until they’re large enough to be out of danger.

If you don’t want to isolate the fry, you can provide them with hiding places in your tank. Vegetation, gravel, and driftwood will provide excellent safe spots.

Keep in mind that prolonged isolation is unhealthy. After two days, you should return your pregnant Swordtail to the tank. You can introduce the fry once it has grown to a size that can’t be considered food.

Provide Good Nutrition

Now that the fish is isolated, it won’t be as hostile anymore, especially when it comes to food. To sustain a healthy pregnancy, your pregnant Swordtail fish needs to feed well.

However, you should avoid overfeeding your fish. Because fry occupies so much of the fish’s body, she can’t feed much. Feed your pregnant Swordtail only three to four short meal servings per day.

There are a variety of meals that could benefit your pregnant fish. Brine shrimp and other live foods are ideal for your pregnant Swordtail. Protein, Vitamin A, and Vitamin D are all abundant in them. These nutrients will ensure that your fish gives birth to healthy fry.

You can also serve your Swordtail premium flakes to eat. Spirulina flakes are beneficial to fish as they boost their body’s immune system and help them fight illnesses. They also include a lot of plant-based proteins in them.

Maintain The Water’s Quality

Partially changing the water in your aquarium is encouraged. However, significant water changes might cause issues. Poor water circulation can degrade aquarium water quality and harm fish.

Any changes in the water quality might cause stress to your pregnant Swordtail. The stress may result in infections or possibly the loss of the baby. Hence, water quality is an important consideration when caring for your pregnant fish.

A good rule of thumb is to change 10% of the water every week and 25% every two weeks.


Monitoring the temperature is important. You should maintain a temperature of 74 to 80 degrees Fahrenheit. You can use a stick-on thermometer to monitor the temperature quickly and conveniently.

A heater can be used to keep the temperature stable. Some heaters offer basic warmer-colder settings. You can modify the settings until your tank’s temperature is at the desired level.

pH Levels

Minor pH levels fluctuations in the water might have a major health effect on your fish. The gills of your Swordtail may be affected by high alkaline levels. In addition, acidic water can cause your fish to produce excessive mucus.

Maintain a pH range of 7.0 to 8.4. Baking soda may easily be used to modify the ratios. The pH of the water changes throughout the day. It’s recommended to measure the levels during the mornings and afternoons.

Start by removing the Swordtail from the tank. Then, apply the baking soda to the water to raise the pH levels. One teaspoon of baking soda per five gallons is advised as it’s a safe amount for slight increases.

Use peat moss to reduce the pH of your water. Place the peat moss in a mesh sample and put it in the filter. The pH will slowly be lowered by the peat moss.

Changes in pH should never be made abruptly, or in significant amounts, since this will harm your fish.

Wrap Up

It may appear strange that your female Swordtail is hostile. The most common explanation, though, is that your fish is pregnant. You can tell whether she’s pregnant by its appearance as well as social behavior.

It’s better to keep the fish isolated until she gives birth to avoid problems within the aquarium. And, of course, you must look after it and the fry until they’re both returned to the public tank.

Once you’ve created a good environment for your fish, you’ll notice that the Swordtail has become calmer.