Are Swordtail Fish Aggressive?


Are Swordtail Fish Aggressive?

Many aquarists find themselves in crossroads when it comes to defining the nature of their swordtail fish.

In a number of cases, you will hear complaints about this tropical fish species becoming overly bullish and dominant.

Sometimes, they will push everyone and take over everything including the sinking flakes or push and chase away other fellows in the tank.

In fact, you may wonder whether you chose a bad seed or whether you are the one suffering alone.

So, are swordtail fish really aggressive? Swordtails are peaceful in general and will remain peaceful as long as their habitat is adequate. They are exclusively peaceful tropical fish species. In fact, for any beginner, swordtail remains an ideal fish to start with since they are hardy and can survive under wide range of condition.

However, there are a number of reasons that can force your swordtail fish to exhibit aggressive behavior. In most cases, you will realize that male fish tend to become more aggressive to their male counterparts.

This also applies to female swordtails. It is a territorial thing. In some other instances, a slight change in water perimeters can result in dominance and aggression.

That’s not all. There are several other reasons why your swordtail fish can one day wake up only to start exhibiting aggressive behavior. Let’s take a look at these factors.

Aggressive Behavior Between Swordtails

Understanding whether a specific fish is aggressed or not depend on how they act. Maybe you can be in the know or not. But how does a bullish swordtail fish acts?

A bully swordtails fish regards themselves as the gods in the tank. They want to be revered to. They will chase other innocent and shy looking counterparts to the wrong directions. Just like the lions in the jungle, these bullies tend to demarcate their territories. And, they tend to fight tooth and nail to keep their territories against invasion or intrusion by fellow tank mates.

But are bullies born like that? Definitely not…

You can sleep with peaceful and harmonious pets in your tank only to wake up the following day and find out that the tank is turned into a ring. To your surprise, you will realize that it is not always the larger fish that bullies the smaller ones. It can be the reverse.

It is advisable to spot the bully and remove it from the tank. Such bullies when placed in a lonely tank for some period of time, they tend to calm down after which you can be free to send it back to the original tank. On the other hand, you can also remove the bullied fish in order to remain with only the bully and the females.

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 more so to the fins of the bullied fish hence affecting their general life activities such as swimming and breathing.

Common Cause of Aggression in Swordtail Fish

From my research and experience, I found that most of the time, sowrdtails will become aggressive due to overcrowded tank, inadequate male to female ratio, small swimming space or pregnancy. Now let’s discuss each one in more details:

Overcrowded Aquarium

In natural habitats such as in the river, lake or ocean, different fish species tend to remain harmonious and live peacefully since they have adequate space for themselves. On the other hand, they do not need to scramble for them to acquire the basic resources for healthy living.

In an aquarium tank, the space is so limited. And, since the tank is overcrowded, stronger swordtails will draw their territorial boundaries. Therefore, any fish that crosses their boundaries is always chased and fought even to death. Second, in a crowded tank, the swordtails remain stressed and always aggressive.

To avoid overcrowding, you can go for a larger tank or keep recommendable number of fish in the available space. You should also not include many things in the tank in order to maximize the use of the available spaces.

Remember, swordtails are excellent swimmers. Always ensure the space available, can easily accommodate each individual fish without any scramble.

Aggressive Pregnant Female Sowrdtail

Pregnant swordtails fish tend to be stressed. It is this stress factor that elevates their aggressive rates. Second, due to the added burden, pregnant swordtails are always lonely, usually at the bottom of the aquarium. Their movement is limited to specific places. Due to this factor, they will not want to be interrupted.

Any fish that tries to interrupt the pregnant fish is always chased and fought. Due to their critical condition, it is advisable to keep the pregnant swordtail fish in a separate tank until it gives birth to the livebearers. This will not only help to protect her from stress and interruption but also enable you to monitor her during the pregnancy hence giving you ample time to protect the livebearers from being eaten upon birth.

Male to Female Ratio

It is of gross importance to keep a proper male to female ratio. With more males in the tank, chances are that they will ever be fighting against each other. Same happens to female swordtails.

On the other hand, when the female swordtails reach sexual maturity, the male counterparts always follow them for mating. During this time, scrambling occurs hence, the stronger male will dominate and develop aggressive behavior towards another male.

Small Swimming Space

Just as aforementioned, swordtails are ideal swimmers. They can be as few as you may think, but in reality, your tank may not fit them due to their outstanding athletic zeal. On the other hand, the fish may need hiding places.

Using live plants provide them with covers. Your main objective is to maintain an aquarium that looks exactly like the natural habitat. With that, your swordtail will live a stress-free and healthy life.

Why are male swordfish fighting?

Male swordfish fights to maintain their territories. Just like any other animal, they feel the need to keep specific places in the aquarium to themselves. Hence, they will do whatever is necessary to maintain these specific areas.

Secondly, the alpha male may fight other sub-males for mates. With time you will realize that there is this one male that swims closer to the female swordtails. This happens when the female swordtails are ripe for mating.

It is the nature of the sub-male swordtails to remain in a specific corner, stressed and unable to retreat. When they are smaller and haven’t grown the longer sword-like tail, you may confuse them to females.

Why swordtail fish chase each other?

Swordtails are generally harmonious and in most circumstances, they gleefully swim up and down the aquarium without disturbing their mates. However, you may spot a swordfish chasing another while at the same time nipping it. Such scenes are always bizarre and, if you are a newbie aquarist, you may think in the wrong way.

There are two reasons why a swordtail fish can chase the other one. One, an alpha-male can chase the female partner to mate. Therefore, it is very important to consider gender mix since it affects the overall behavior of the pets in the tank.

The second reason why a swordtail may chase another one is during the verge of marking its territory. The fish have personalities that resemble ours. The stronger males will always dominate over the weaker sub-males.

Having noticed this, it is advisable to remove the alpha-male or the sub-male from the tank and place it in another tank before it is too late.

Can swordtail kill each other?

Yes. There are cases when swordtail fish will kill each other. An alpha-male that has decided to express dominance to other sub-male can be a real pain in the back. He will relentlessly chase the other sub-male any time even in the wrong direction.

As a result, other sub-male will remain stressed and vulnerable to diseases. Under such conditions, the sub-male always dies due to the stress factor.

Second, it is the norm of the fight that the alpha male will keep nibbling the tail of the sub-male. This usually results in serious injuries that lead to the death of the sub-male.

You will realize that all the above methods relate to one thing, minimizing stress in the aquarium. Bottom line, the condition created in the aquarium should look exactly like the natural fresh-water condition and your fish will live harmoniously and peacefully in the tank.


Swordtail fights are usually a common problem that is reported often by many aquarists across the globe. It is the indication of the tank harboring aggressive swordtails.

However, since you like your pets, do not wait and see them die on the hands of the alpha-males.

In order to minimize the rates of aggression among the fish species that you keep inside the aquarium, first understand the main cause of the aggression. After that, take the necessary step in solving the problem.

Some of the most approved ways of solving aggression problem in your tank include; Removing and isolating the bully, removing the sub-male, maintaining a proper male-female ratio, avoiding overcrowding in the tank to create space, and testing ammonia level.

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