Why Is My Guppy Bullying Other Fish? (6 Easy Solutions)

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Guppies are pretty hardy creatures, which is why I enjoy growing them in my aquarium. However, their behavior could be unpredictable. For example, more than once, I’ve noticed that my guppies consistently bully and chase their tankmates. To solve that issue, I began researching the reasons for it pretty profoundly.

Guppies typically bully and chase other fish for mating purposes. That usually occurs between male guppies and females, possibly from different species. However, guppies also go after their tankmates due to stressful conditions, including low water quality, lack of food, and hierarchy establishment.

As we move forward in this article, I will share a few tips that are likely to stop your guppies from bullying other fish. I will also share the precise equipment that I use, which allows me to maintain ideal water conditions and healthy fish.

Also Read: Stress In Guppy Fish

Why Do Guppies Chase Each Other & Other Fish?

Guppies are not known for their aggression. On the whole, they are pretty peaceful fish. Yet, they are more than capable of bullying their tankmates. That includes other guppies and fish from different species. 

If your guppy is making life in the tank a nightmare for other fish, the following are probably to blame:

1. Fun and Entertainment

Chasing guppies aren’t necessarily bullying their tankmates. Like any other pet, guppies are playful. They enjoy running after one another. It would be best not to associate this behavior with aggression until you identify additional evidence supporting your presumptions.

It would be best if you also observe what your guppy is practically doing. If all it does is swimming by its tankmate, I wouldn’t worry too much about it. However, if your guppy also nibbles on its companions, or you notice signs of injury, there is probably more to it.

2. Mating Purposes

If the aggressive guppy is male and the victim being bullied is female, you have probably witnessed a mating ritual. Male guppies are smaller and more colorful than their female counterparts. If a smaller, more colorful fish is chasing a more prominent, less colorful fish, the male guppy is most likely vying for the female’s attention.[1]

On the one hand, this behavior is natural and healthy. On the other hand, if you have more male guppies than female guppies, your male guppies’ mating habits will mimic bullying. That is to say; they will badger and harass the female guppies to the point of exhausting and potentially killing them.

3. Dominance & Hierarchy

If your tank features female guppies, some male guppies will likely attack other male guppies as a way of securing the right to mate with the females. In a male-only tank, the males can still engage in aggressive behavior to establish their dominance.

Typically, you will notice the most massive guppy chasing smaller tankmates. Bullying of this sort is most dangerous in tanks with a small community of guppies because one or two fish could become the target of all the aquarium’s hostility.

4. Poor Tank Conditions

Poorly maintained tanks can encourage hostility in guppies. Temperatures that are higher or lower than the ideal, the wrong pH, and the presence of toxins such as ammonia can induce stress in fish. And stressed fish tend to attack their neighbors. 

Guppies are no different. If your guppy is suddenly misbehaving, test the water to ensure that all the parameters are within the appropriate range.[2] You should suspect that this is the case if your tank appears dirty due to debris and waste.

Ideally, the water requirements of guppies include:[3]

  • Water temperature: 72-82 degrees F.
  • Water pH: 6.8-7.8.
  • Water hardness: 8-12.
  • Ammonia, nitrates, and nitrites should be around 0.

5. Lack of Food

If your fish are starving, the strongest guppies will bully their weaker counterparts for more meal portions. If the scarcity persists, the aggressive guppies will become more violent towards other fish, competing with them over food.[4]

If that is the case in your tank, your guppies will likely calm down after their daily meal arrives. You may see this behavior if you’ve been skipping meals, or the portions are too small to meet the needs of your tank.

Also Read: Why Do Guppies Lose Their Color?

Are My Guppies Fighting or Playing?

It is essential to differentiate between fighting and playing with guppies. If your guppies are fighting, you must intervene before the weaker fish suffers irreversible damage. However, if they are merely playing, it would be best to leave them alone. 

To distinguish between the two, you should first look for signs of aggression since they are much easier to identify. They include:

1. Injuries and Wounds

Look for the physical consequences of violence on the victims. That includes torn fins and tails, dislodged scales, and any other marks on the fish that show that it was assaulted. Fish that have suffered physical harm should concern you. 

A guppy is unlikely to die from a nipped fin, but such injuries can attract infections and parasites that can lead to death over time. Like in humans, fungi and bacteria are more likely to grow on exposed areas such as wounds and scratches.

2. Timidity

There is nothing wrong with one guppy chasing another. However, if the guppy being chased develops timid mannerisms, you can conclude that it feels threatened. Guppies that have been bullied spend a lot of time hiding and cowering.[5] 

Some of them stop eating because they are too frightened to mingle with the other fish during mealtimes. They will prefer to stay at the corner of the tank and grab leftovers that have sunk to the substrate. Sometimes they will go inside caves and decorations.

3. Established Territories

If the chasing guppy is indeed bullying its victim, you may notice that certain areas in the aquarium have turned into territories. You will typically see the bullying guppy spending its time there, chasing around fish that have entered its territory.

That could also happen in groups. Sometimes several guppies become a unit and choose to leave one guppy behind. The underdog is usually smaller and features pale colors. That victim is unlikely to breed with the females since competing with the aggressive groups is too challenging.

Also Read: Why Is My Guppy Shaking?

How Do You Stop Guppies From Fighting And Being Aggressive?

Keeping your guppies from fighting involves these steps:

  1. Test your water for ammonia, nitrates, nitrates, and pH.
  2. Perform 15-25% water changes weekly.
  3. Keep at least three female guppies for each male.
  4. Get a relatively large tank, preferably 20 gallons and over.
  5. Introduce plants and decorations for hiding spots.
  6. Rearrange the aquarium to reset preexisting territories.

It isn’t always possible to maintain the peace in a guppy tank. Some guppies have aggressive personalities, and they won’t change. But it would help if you only came to such conclusions after trying the following:

1. Improve Your Tank’s Conditions

As was noted above, stress encourages violence among fish. If you want your guppies to live peacefully, it would be best to maintain the appropriate parameters in their tank. A healthy environment is likely to lower aggressive behavior.

Start with installing a heater to maintain the temperature. You should also get a high-quality filter to control the waste. On that matter, I highly recommend the MarineLand Penguin Bio-Wheel Power Filter (link to Amazon). It gets the job done and almost doesn’t make any noise.

I also suggest considering the API Aquarium Test Kit (link to Amazon). That simple, affordable bundle quickly measures your pH, ammonia, nitrates, and nitrites. Within minutes, it will tell you if you should perform more frequent water changes.

Bear in mind that a healthy tank will produce healthy fish that have healthy habits. Aggressive guppies will likely stop chasing their tankmates once you improve the water conditions. Replacing 15-25% of the water weekly will get the job done.

Regarding their feeding habits, guppies are not picky eaters. However, it is essential to provide them with a sufficient amount of food. Make sure that you give them the amount they can consume within two to three minutes. I also suggest considering an automatic feeder, such as the Eheim Automatic Feeding Unit (link to Amazon).

2. Get the Right Male-to-Female Ratio

Your male guppies shouldn’t outnumber your female guppies. It is best to keep at least three female guppies for every male guppy. That is the best way to prevent male guppies from fighting one another for the female’s attention.

You also have to option to grow merely females in your tank. That will also prevent reproduction if you wish to keep the same number of fish in the tank. Females are larger than male guppies, and distinguishing between the two is pretty straightforward.

3. Pick the Right Number of Fish

Because guppies have a reputation for fighting one another for female guppies’ attention, some aquarists believe that it is impossible to maintain male-only guppy tanks. However, that isn’t entirely true. 

A male-only tank is prone to violence, but only if you don’t have enough guppies. The few fish in the tank will eventually gang up on one or two unfortunate guppies. Hence, if you wish to keep merely male guppies, grow them in groups of at least eight. That will dilute their aggression.

4. Choose the Right Tank Size

Try to match the size of the tank to the number of fish. Guppies need at least 5 gallons.[6] But you shouldn’t hesitate to invest in a bigger tank if you realize that your guppies are overcrowded. Aggressive guppies are less likely to lash out at their tankmates if they have ample space to roam.

5. Add a Few Plants & Decorations

Your tank should have plenty of hiding places. That includes plants, caves, rocks, pots, logs, and the like. That will give bullied guppies some peace of mind because they can go into hiding whenever aggressive guppies approach.

That will also allow female guppies to get some rest from the male ones. However, bear in mind that male guppies might chase even pregnant guppies for breeding purposes. Plants with broad leaves or tall decorations will keep them out of sight. 

Either way, make sure that you don’t overstuff your tank. Decorations can be useful, but if your fish have nowhere to swim, aggression will arise. It would help if you kept the delicate balance between hiding spots and potential swimming areas.

6. Reset Preexisting Territories

Some people believe that you can rehabilitate the aggressive guppy by moving it to a bucket for a few hours. The idea is to disorient the aggressive fish. Once you return it to the main tank, it is less likely to retain its negative habits. This tactic works best in tanks whose guppies are aggressive towards new fish.

If that doesn’t work, you can try changing the tank’s environment by rearranging the plants and decorations. That will also disorient territorial guppies, destroying their old territories, and allowing new fish to establish themselves


In some cases, guppy fish might chase other fish or other guppies out of fun and entertainment. If that is the case, the chased fish should appear healthy, without any signs of injury or lethargy. You shouldn’t worry much if your fish are merely playing.

However, if you also see nibbling signs, such as ripped fins, sluggish behavior, and timidness, you should act accordingly. The immediate solutions would be testing the water and performing more frequent water changes. If that doesn’t work, consider separating the bullying guppy or rearranging existing territories.


  1. https://guppyexpert.com/guppies-aggressive-fish/
  2. https://www.cuteness.com/article/stop-fish-bullying
  3. https://guppyexpert.com/guppy-fish-care/
  4. https://blog.ferplast.com/en/why-do-fish-chase-each-other/
  5. https://seatechaquariums.com/how-to-tell-if-fish-are-playing-or-fighting/
  6. https://www.fishkeepingworld.com/guppies/