Are Swordtails Aggressive? Let’s Find the Answer Together!

Swordtails are considered among the most peaceful species in many fish species.

Their gentle nature has made them an excellent option for both first-timers and veteran aquarists.

The un-hostile and amicable temperament, along with their unique looks, will surely make these fishes a fantastic addition to your aquarium.

But it is not always the case. Swordtails can change their nature, though very rarely. So, are swordtails aggressive? Let’s find the answer!

Are Swordtails Aggressive?

Although swordtails are sociable, peaceful fish, sometimes they turn out to be aggressive and territorial.

If there are a lot of males, it could lead to rivalry when they reach maturity.

In addition, pregnant swordtails may exhibit aggression. Moreover, a swordtail can also fight to the death if it feels its territory is threatened.

Causes of Aggression in Swordtail Fish

Causes of Aggression in Swordtail Fish

Several reasons make gentle swordtails aggressive, and we’ll cover the most common in this section.

Overcrowded Fish Tank

In their natural habitats, such as an ocean, lake, or pool, swordtails are generally peaceful and less aggressive because they have enough space.

However, the same does not go for your aquarium. When you put too many fish in an aquarium, stronger swordtails will set the boundaries of their territory.

Hence, these swordtails will hunt any individual that crosses their boundaries and fight even to the death.

So you can solve this situation by transferring your swordtails to a larger tank or putting the right amount of fish in the space of your aquarium.

Female Swordtails Become More Aggressive During Pregnancy

Female swordtails tend to be stressed during pregnancy, which causes aggression during this time.

Therefore, you should keep pregnant swordtails separately in one tank. It allows you to prevent them from stress and monitor them throughout the pregnancy.

You will also promptly protect the baby swordtails from being eaten upon birth.

Fighting for Reproductive Rights

During the breeding season, males tend to be more aggressive when competing for mates as a natural instinct. It is common if you don’t keep males and females in the correct ratio.

Inadequate Diet

Swordtails are aggressive eaters. So it is essential to ensure an abundance of food available for these fishes.

If you don’t provide enough food for them, swordtails may begin acting aggressively.

We recommend feeding your swordtail fish at least a couple of times per day with supplements that are rich in fiber and proteins. That way, you can reduce their hostility.

How to Determine if Swordtails Are Aggressive?

swordtails are chasing

Aggressive actions like nibbling and chasing other swordtails are a part of the typical mating/playing ritual.

Instead, severe fighting often comes with distinctive behaviors, such as:

  • Nipped and damaged fins.
  • Weaker swordtails typically hide in ornaments or plants and tend to be isolated when bullied.
  • A swordtail died but not for natural reasons.


Can Swordtails Kill Each Other?

The answer is yes. When a swordtail perceives another individual encroaching on its territory, it can pursue the invader and fight to the death.

Also, during combat, a swordtail often bit other fish’s fins. The parasites and bacteria can then enter the body of the injured fish through the wound, leading to infection and eventually death.

Although swordtails can sometimes kill each other or other small fish, this is very rare. So worrying too much about this problem is unnecessary.

Do Swordtails Consume Their Babies?

Yes. If you do not intervene in time, the parents can eat their juveniles.

Similar to most livebearers, swordtails lack parental instincts and often mistake their fry for food.

So it is essential to keep your baby swordtails safe until they are big enough.

Here are some solutions to protect juveniles from being eaten by their parents:

  • Separate pregnant swordtails at the time of spawning.
  • Place live plants in your aquarium to deliver hiding places.
  • Invest in a breeding box.
  • Remove the parents after giving birth and keep baby swordtails separate until they are big enough.

What Should I Do With an Aggressive Swordtail?

We recommend keeping it alone in another tank for a few days to a week and seeing if it calms down. If this swordtail remains aggressive after that, you should remove it to avoid it continuing to injure other fish.

What Should I Do With My Bullied Swordtails?

If you find that your bullied swordfish has signs of infection or injury, you should start by moving them to another tank to avoid infecting other tank mates.

Put these swordtails into quarantine, closely observe and take care of them properly to prevent further infections.

If the wound is severe, you will need the help of a veterinarian.

How To Tell If A Swordtail Is Female Or Male?

The male is the only swordtail with an extension of the tail fin. Meanwhile, the female sports a rounded tail fin like one hand fan.

When it reaches maturity, the female body tends to be more rounded and larger than the male.

Can I Keep Two Male Swordtails?

It is feasible to keep two male swordtails in the same aquarium. But we recommend keeping five to six ones to reduce possible aggression.

The fewer individuals in your aquarium, the higher the chance they will go berserk on each other. So you should not keep two males in a tank.

Is It Okay To Maintain a Tank With Only Male Swordtails?

It is feasible, and our suggested number of males is five to six. When there’s a mix of females and males, it is wise to keep the number of females higher than males. A larger aquarium also helps reduce conflicts between males.

The Bottom Line

Although swordtail fishes are typically peaceful, sometimes they can be aggressive. It could be due to several reasons that we mentioned above.

If you notice a misbehaving fish, you should separate it from the rest of the tank for about a week or so. Then put it in the tank, and you can expect a happy aquarium.

Thanks for your time!