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Are Killifish Aggressive? Everything You Need To Know!

With the bright colors of killifish as well as their falling prices, the popularity of keeping killifish within the fish keeping community has been increasing for a number of months now.

As the popularity of keeping pet killifish keeps on increasing, the number of people asking various questions about killifish has also been increasing.

One of the most important things to factor in about keeping a killifish is their aggression levels and we see countless people reaching out to ask if killifish are aggressive or not each month.

Due to this, we have decided to publish this article going over the aggression levels of killifish as it will usually depend on the specific type of killifish you want to keep in your tank as well as your tank setup.

There are a number of different aggressive killifish species that can often be calmed provided you set your aquarium tank up correctly but we will cover that in more detail later in this article.

Are Killifish Aggressive?

Most species of killifish are aggressive and can chase their tank mates or nip their fins with this usually being normal behavior for many of the bright and colorful species of killifish.

As the majority of people who do want to keep killifish in their tank often settle on the brighter, more colorful killifish, they usually have to take steps to try and manage the aggression of their fish once in their tank.

Due to there being so many different types of killifish that are becoming more and more popular within the fish keeping hobby, we actually want to take a look at some of the more commonly kept types of killifish and their aggression levels.

This should be able to help as many of our readers as possible get a better idea of what to expect with the various types of killifish.

Pike Killifish

Pike killifish are usually aggressive and will chase and nip their tank mates relentlessly. In some cases, pike killifish will actually eat their tank mates as well as other pike killifish too so we don’t recommend you keep them unless you are an experienced fish keeper.

Blue Gularis Killifish

Blue gularis killifish do tend to be aggressive in most tank setups and male blue gularis killifish can end up being hyper aggressive unless they are kept in a tank that is large enough for them.

Females are still aggressive but tend to calm down in larger tanks with plenty of sight breaks when kept in groups of two or three.

Clown Killifish

Clown killifish tend not to be aggressive in most tank setups making them the ideal tank mate for beginners who want to keep a killifish for themselves.

The clown killifish is actually our recommendation of choice when it comes to keeping a killifish and betta fish with each other and they are one of the few beginner friendly killifish available.

Golden Wonder Killifish

The aggression levels of golden wonder killifish will usually depend on their tank size and tank mates.

If all of their tank mates are around the same size of your golden wonder killifish, they tend not to be too aggressive but they will chase, nip, and even eat smaller fish in their tank.

Gardneri Killifish

In most tank setups, gardneri killifish will usually be peaceful and not cause problems with aggression in their tank with their tank mates.

If the fish ends up stressed then you may have problems with some mild nipping and chasing but this really is rare with this type of killifish.

Black Pearl Killifish

Male black pearl killifish can be hyper aggressive to anything in their tank so they are not recommended for beginners but the females are not usually as aggressive as the males.

That said though, in most situations, we really wouldn’t recommend a beginner gets a male or female black pearl killifish until they have some experience with fish keeping.

Turquoise Killifish

Due to the dull color of female turquoise killifish, most people only want the males in their tanks but male turquoise killifish can be very aggressive to anything in their tank with them.

They are usually not recommended for a community tank and most beginners should avoid them in our opinion.

Rachovii Killifish

Male rachovii killifish can be very aggressive to other male rachovii killifish but this aggression doesn’t usually tend to be passed over to other species provided the tank the fish is in is large enough.

Many people opt to keep a rachovii killifish in their tank for their beautiful look and although they are usually not aggressive to other fish in their tank, we would only recommend them for people who have experience with the fish.

Normans Lampeye Killifish

There are usually some minor issues with aggression from male normals lampeye killifish towards other male normals lampeye killifish in the same tank but it is usually just minor chasing and fin nipping.

For the most part, the normans lampeye killifish is a great killifish to keep and we usually recommend them as one of the better options for people who are new to keeping killifish in their tanks.

American Flag Killifish

In most tank setups, american flag killifish are not aggressive unless they are getting ready to spawn but even then, their aggression levels are usually low when compared to other types of killifish.

This makes them a great option for a number of different tank setups provided you have a tank that is large enough for the species.

Seminole Killifish

Both male and female seminole killifish can have issues with food aggression in their tank and if you are accidentally underfeeding the fish in your tank then this really can end up causing some potentially serious problems.

There can be some less serious issues with aggression when it comes to keeping a seminole killifish too making them tricky for beginners to keep without having problems with aggression.

Woworae Killifish

Provided your woworae killifish are kept in a tank where all of their tank mates are the same size as them or larger, you shouldn’t have problems with aggression.

If you want some fish species in your tank that are smaller than around one inch then your woworae killifish may chase and nip their smaller tank mates constantly.

How Can You Reduce Killifish Aggression In Your Tank?

If you have your hear set on keeping one of the more aggressive types of killifish in your aquarium tank then you are able to try a few things to reduce the chances of the fish being aggressive towards their tank mates.

Here are the four main things that we would usually recommend and we will cover them in more detail later in the article:-

  • Fish Hides!
  • Live Plants!
  • A Large Tank!
  • Avoid Overstocking!

Ideally, you will be trying to implement all of the above if possible as you will often need all the help that you can get when it comes to aggressive killifish species.

Fish Hides!

If you provide your fish with somewhere to hide away from their tank mates then this can really help to reduce the aggression levels in the tank.

It is important that there are enough hiding places for all of the fish in the tank though as if there isn’t then the more aggressive fish will often claim all of the hiding spots for themselves which can make the situation even worse.

We would usually recommend that you have one fish hide for every two or three fish in your aquarium and this will give each fish their own place to hide away when they need to.

Live Plants!

Another great way to reduce aggression levels in your aquarium is to add some live plants into the tank as these can provide the fish with plenty of places to hide away from their tank mates.

Long growing plants are always excellent options for both hiding places and sight breaks with there being a number of very popular types of plants you can use.

Even the shorter live plants can work well in some setups too but you will usually need rocks to help act as a sign block for shorter plants.

If you don’t want to add live plants to your tank then there are some surprisingly high-quality fake plants on the market these days that you can try too.

A Large Tank!

Different killifish have different lengths and different levels of aggression meaning that they usually need very different tank sizes to each other.

Many people new to keeping killifish fail to realize this and accidentally put their killifish in a tank that is far too small for them with this usually resulting in aggression.

Always make sure that your tank will be large enough for the killifish you want prior to purchasing it to help prevent issues with aggression in the future.

Avoid Overstocking!

We have noticed a number of people accidentally overstocking their killifish tank resulting in their killifish getting stressed and acting aggressively.

This can even be a problem for a less aggressive type of killifish with many people not realizing just how big of a part stress levels play in fish aggression.

Always try to make sure that you unstock any tank if possible, especially a tank that has any type of killifish in it.

Which Killifish Are Not Too Aggressive?

As we covered earlier in our article, there are a number of killifish that are not too aggressive towards their tank mates making them the better option for beginners or people who want a peaceful community tank.

The best killifish that are not too aggressive are:-

  • Clown Killifish
  • Gardneri Killifish
  • Normans Lampeye Killifish
  • American Flag Killifish

As we mentioned earlier in the article, provided you make sure that none of the tank mates in the aquarium are smaller than them, Woworae Killifish and Golden Wonder Killifish can sometimes work well too.

Both the Woworae Killifish and the Golden Wonder Killifish tend to only be aggressive to smaller fish than them so if everything in the tank is their size or larger, they tend to calm down.

Are Killifish Fin Nippers?

A lot of people new to keeping killifish worry that their fish will be fin nippers but as we covered in our breakdown earlier in the article, not all killifish will nip the fins of their tank mates.

It can be common with some species but if you stick to the less aggressive types of killifish then it shouldn’t really be an issue for you in most cases.

Still it is always something to consider and if you do have one of the calmer types of killifish that is stressed out then they may start nipping fins too.

Do Killifish Eat Other Fish?

Most types of killifish tend not to actually eat other fish and chasing or fin nipping will be the main issue for your tank.

Still, some of the larger types of killifish will eat some of their smaller tank mates so you do have to keep this in mind when planning out your aquarium setup that involves a larger type of killifish.


We hope that you enjoyed our article on killifish and their level of aggression.

Provided you plan out your aquarium setup with your killifish prior to purchasing the fish then in most cases, you really shouldn’t be having any real problems with aggression.

If you have any questions or comments then please feel free to leave them below.

Happy Fishkeeping!