Will Swordtails Kill Each Other? 4 Reasons Why They Can And How To Prevent It

Will swordtails kill each other?

Swordtail fish are small and very active fish, they could only grow up to 5.5-7 inches in size. They are loved by many aquarists because they are considered to be non-aggressive, fast, active, and very active algae eaters. There is a popular belief that these fish will normally kill each other when kept together, despite being tagged peaceful, so this has made many aquarists stay away from keeping them in their numbers. In this article, you will learn if they could kill themselves or not and why they might.

Will Swordtail Fish Kill each other? Swordtail fish will sometimes fight each other to show dominance. They might end up hurting and even killing each other.

These types of fish are very active and lively in the aquarium, and they are very fast too, they are considered to be peaceful by many people, but they could sometimes change totally from that narrative and become very dominating and aggressive too.

This act is often seen in the males more than in the females, although, the females could sometimes become aggressive too due to some reasons, which you will learn later in this article.

Normally, Swordtails could be kept together, but due to some reasons, which you will also learn in this article, they might become very territorial and fight among themselves, which could lead to the death of some of them.

Some may turn to bullies. Bullying causes stress to other fellow fish, as a result, the bullied fish will be rendered vulnerable to tropical fish diseases due to the stress factor.

Bullying can also result in injuries and more to the fins of the bullied fish, hence affecting their general life activities such as swimming and breathing, etc, and might even kill the fish.

Swordtails will kill each other, but it is not intentional because they do it as a result of fighting and fin nipping.

Why Swordtail Fish Fight Or Might Become Aggressive

Swordtails could sometimes become aggressive, despite being regarded as peaceful fish.

There are many reasons why they could turn from being peaceful to being aggressive and territorial, which could lead to fighting and killing each other.

1. Poor ratio of Males and Females in the tank: It is normal for every male animal to try to prove dominance and take as many females as possible, these fish often do it to get as many females to mate as possible.

There is a widely accepted ratio to keep in a tank for peace to reign, which is a ratio of 2- 3 females per male.

What this means is, for every male you introduce to the tank, there should be 2 or 3 females for it, etc.

By so doing, the males will have enough females to male, hence there will not be any need to be dragging the females and showing dominance to chase other males away and get the females for themselves.

2. Poor Tank size: Do you know that one of the things that breed aggression in animals is the size of their habitats?.

Well, this is very common for aquarium animals especially fish, which swordtail is one of them.

Naturally, fish like to stay in an environment where they are very free and have vast territories, especially territorial fish.

Swordtail fish are very fast and active, despite their small size, they are still faster than most freshwater fish, even if they swim backward.

So, Such fast and active fish requires a lot of swimming space, that’s why it is recommended to keep them at least in 15-20 gallons per fish so, that they won’t become aggressive.

So, if your Swordtails, especially the males are showing some signs of aggression and territorial, etc, you need to check your tank size and find out if you have overstocked them.

3. Wrong Water Parameters: Apart from tank size, another factor that could trigger the aggression of many aquarium animals is poor water quality.

Poor water quality could be a result of dirty water, chemicals in the water, and even temperature.

Their ideal water parameters are:

Water Condition Hard, Alkaline water(12-30dGH)

Water Temperature 65-80°F.

pH up to 8.2.

Tank Region – Usually found dwelling along the mid and top section of the tank.

When the ideal water parameters are not in place, making the water unsuitable for them, they will become aggressive and might start attacking each other as a result of stress and frustration.

It has been noted that an uncycled tank is one of the reasons or causes of this behavior in fish and other aquarium animals.

4. The female Swordtail fish could sometimes become aggressive and will start attacking others, and even any creatures that might come closer to her.

This particular behavior is natural because it is caused by stress and frustration as a result of pregnancy.

Swordtails are livebearers, so when they become pregnant, they are always harsh and aggressive toward each other.

Also, Both male and female swordtails will feed on their fry, so try to keep the adults off to give the babies the chance of survival.

So, if your Swordtails are attacking themselves and maybe, as a result, killing themselves, then these are the possibilities or why they are doing that.

How To Keep Your Swordtail Fish From Becoming Aggressive And Avoid Killing Each Other

You have learned the reasons why they are aggressive, now here are the tips to curb their aggression.

1. Keep them at a normal ratio: This means keeping the recommended number of males and females in the tank, to curb the level of dominance and fights intended to get the females all to themselves.

When a normal ratio is kept which is 1 male vs 2-3 females, they will have enough females in the tank to mate with, hence there won’t be any need for fights to get the females because every male will now have enough females on his own.

2. When getting a tank, get a very big tank that will be able to contain them, depending on the number you want to keep.

The recommended tank size for each swordtail is 15-20 gallons, so try to buy a sizeable tank that will successfully house them all without them struggling for space.

In this case, they will stay out of each other’s way.

3. Make sure your tank is planted and has some hiding places like caves, pipes, substrates, etc.

All these are necessary because they will normally hide and avert the possible wrath of others.

Again, the fry will hide in them to survive, and the plants might keep the adult fish busy, and they would hardly notice other fish.

4. Try as much as possible to get any aggressive fish, be it male or pregnant female out of the tank, or better relocate the less aggressive ones so they will not be harmed.

It has been proven that once an aggressive fish is kept all alone, it will become less aggressive and dominating.

So get the aggressive ones out and reintroduce them back to the former tank after some days or weeks, and they will be calm and tolerant.

5. Make sure your tank is fully cycled and the ideal water parameters maintained so that your fish will be comfortable.

Why Do Swordtail Fish Chase Each Other?

Swordtails sometimes chase each other because they want to prove dominance or they want to mate with the females.

If you see them chasing each other, two things are involved, it’s either the male is chasing the female for them to mate, or the males are fighting themselves to prove who is the alpha male and who is the sub male.

So, when the males chase each other, they are fighting themselves for any of those reasons I explained above.

How Many Swordtail Fish Can Live Together?

It is recommended to keep 5-7 Swordtail fish together in a tank, which females being more in population.

These fish could be very peaceful and friendly if everything is normal, and if they have all they want.

So keeping them not less than 10 in a spacious tank is great. So they can live together.

Are Swordtail Fish Aggressive?

No, Swordtails are considered to be very peaceful and tolerant, but they could become very aggressive if they are kept in an unsuitable environment.

They are not usually aggressive, so, two or more swordtails could Peacefully live together in a tank without trying to trouble the other.

Are Swordtails Schooling Fish?

No, they are not schooling fish, but they like to live in groups and could stay on their own too without feeling lonely.

For the fact they can stay together in a tank without disturbing each other doesn’t make them schooling fish, so they ain’t.


Swordtails are very lovely and active fish to keep, but due to certain conditions and reasons, they may become aggressive and territorial and might fight and kill each other as a result of stress and frustrations.