19 Most Aggressive Freshwater Fish For Your Aquarium

Fish are just like any other animal, and aggression can be part of their nature. However, some species are more aggressive than others, and if you bring such a species into your peaceful aquarium, then it can become chaotic for you to handle.

Aggressive freshwater fish can change the dynamics of your aquarium drastically, which is why you really need a separate environment for them.

So if you’re dealing with aggressive freshwater fish or want to know which species tend to get particularly aggressive, keep reading!

Why Do Fish Get Aggressive?

Fish tend to become aggressive when they face problems related to food, territory, and mates. These three things are a fish’s biological needs, and they do anything to protect them, which is why keeping an aggressive freshwater fish in your aquarium can get very difficult.

Here’s more detail about why fish get aggressive:


The main reason for aggressive fish behavior is territorial. Many types of fish need a separate area which they can call their own, and in order to defend this area, they get aggressive. If your tank has any hiding spots or caves, then aggressive freshwater fish will try to take over this area and claim it as their own. Other fish will not be able to make use of these areas because aggressive fish will attack them and push them away.

Mates And Breeding

Both male and female fish also tend to get aggressive during the mating process. When fish court each other, male fish fight each other over the female fish and even get injured. Plus, male fish tend to get carried away during mating and may even attack other fish that resemble them physically.

On the other hand, female fish have a protective instinct, so they tend to get aggressive if anyone tries to come near their eggs. This is why you must opt for birthing tanks so that breeding and mating-related attacks do not take place.


Just like any other animal, fish can also get aggressive when it comes to food. In their natural habitat, smaller fish are lower on the food chain, whereas larger fish view these small fishes as food. This dynamic remains the same regardless of the environment. So when it comes to aquariums, fish tend to become aggressive and compete for food. This usually happens if the tank is crowded and their food needs are not being met properly.

Why Do Fish Get Aggressive

What Does Aggressive Fish Behavior Look Like?

You may have aggressive freshwater fish in your aquarium harassing other fish without even knowing about it. You need to look out for a few specific things to understand aggressiveness in fish. These include:


This behavior is the easiest and quickest for you to note. One fish will attack others by biting them or butting their head into their head. This type of physical attack can scare the non-aggressive fish and keep them hidden for some time.


When it comes to eggs and fish babies, every species has a different approach. Some fish parents have a more laid-back attitude, whereas some defend their newborns aggressively and use all of their strength. Moreover, some parents join together and become aggressive towards anyone who comes near their kids. They will even attack human hands, so you need to be extra careful if you have aggressive freshwater fish in your aquarium.


As mentioned above, aggressiveness in fish is usually due to territory, mating, or food, so it is very easy to notice aggressive behavior during feeding times. Aggressive freshwater fish tend to swim rapidly around and eat as much food as they can. They also steal food from other fish mouths and gills for themselves. To stop this from happening, you need to not only feed an adequate amount, but also spread the food throughout the tank so that it reaches everyone equally.

Aggressive vs. Semi-Aggressive Fish

Aggressiveness in fish can be divided into two types: fully aggressive and semi-aggressive.

While fully aggressive fish are self-explanatory, semi-aggressive fish are mostly docile, but they can become extremely aggressive if they feel threatened. This nature allows semi-aggressive fish to protect their area and resources.

These fish can be kept in an aquarium or community tanks along with other fish, but the tank must have plenty of hiding spaces.

But how are aggressive freshwater fish and semi-aggressive freshwater fish different from one another?

Semi-aggressive and aggressive fish are very different from each other. The former exhibits aggressiveness mostly only under specific circumstances, whereas the latter has extreme territorial issues and must be housed alone.

Moreover, aggressive fish often opt to simply chase their weaker tank mates without any reason, which is why keeping them in community aquariums is not recommended. Aggressive fish require a lot of attention and careful handling, whereas semi-aggressive fish can perfectly fit in community tanks.

But before you go ahead and get aggressive freshwater fish for your aquarium, it is essential to know how to take care of them properly.

19 Most Aggressive Freshwater Fish For Your Aquarium

If you like the thought of keeping aggressive freshwater fish in your aquarium because of how fascinating they can be then you need to know everything about them. Mentioned below are some of the most aggressive fish that you can buy, so keep on reading to learn more about them.


You may have seen piranhas and their aggressive nature in movies. And it’s true! These are one of the most aggressive freshwater fish available today. There are around 20-50 different species of piranhas that exist today, but for indoor tanks, people usually opt for the Red Bellied Piranha.

Piranhas originally come from the Amazon River in South America, but you can find them in other rivers as well. However, this fish is very intolerant of aquarium friends. Plus, a baby piranha requires a tank of up to 20-gallon to live easily.

Once these fishes reach maturity, you will need an even larger tank to house them. Keep in mind that piranhas are omnivores, and tend to eat everything that moves. You can feed them small dead fishes, pellets, vegetables, seeds, crustaceans, and flakes.

If you want to keep more than one piranha, you will have to be consistent with feeding them; otherwise, if they are hungry, they might end up eating each other. Piranhas are illegal to keep in many states, so make sure you are aware of the laws before you buy this fish.


Black Wolf Fish

Black Wolf Fish are found in the Amazon River Basin and are natural predators, which is why they should be kept alone. Their only potential tank mates are similar aggressive fish, but even this friendship can end in a disaster due to their extremely aggressive nature.

Black Wolf fish tend to stay at the bottom of the river in their natural habitat, and keep an eye on prey as they swim by. They are black and brown in color, which allows them to blend in the environment easily and makes hunting prey simple.

If you want to keep these fish at home, remember that they prefer warmer water and live fish and insects as food. The minimum tank size you need to breed this fish is 120 gallons as well, since they can grow up to a massive 20 inches.

Black Wolf Fish


Arowana is one of the most desirable aggressive freshwater fish present today. It is also one of the most expensive and has two different types: Asian Arowana and Silver Arowana.

When it comes to taking care of Arowana, you should be prepared for some challenges because of the nature of the fish. The Silver Arowana can grow up to three feet when kept in captivity and weigh around 4.6kgs. Due to its size and weight, you will need a large aquarium of up to 250 gallons.

Plus, Arowana is a predator fish, which is why finding a tank mate for them can be tricky. These fish do not tolerate other Arowanas in their space, so if you choose the wrong tank mate, the Arowana might eat it up!

But fishes such as Oscars, Parrot Cichlids, Catfish, and Angelfish can live together with Arowanas in peace. Arowanas are carnivores, and you can feed them small fish, insects, and other processed food products. Make sure you feed them on a regular basis; otherwise, your tank will start to look “empty” over time.


Rainbow Shark

Even though the name Rainbow Shark sounds very dangerous, this is not the case for this aggressive freshwater fish. Despite the name, Rainbow Shark is an omnivorous tropical fish. It can grow up to 6 inches long and is found in Thailand.

These fish are only semi-aggressive, so you don’t have to worry about them attacking other fishes in the community tank just because they feel like it. However, this does not mean that they will get along well with their tank mates either. These fish tend to get into fights with even their own species over territorial issues. If you have a good tank size with space for the fish to hide, then Rainbow Shark will keep their aggressiveness to a minimum.

You may mistake Rainbow Sharks for Red Tail Sharks, since they have a similar physical appearance, but the former has red fins as well, whereas the latter only has a red-colored tail. Rainbow Sharks can grow up to 6 inches, and require a tank of at least 50 gallons to grow and thrive.

Rainbow Shark

Afer Knife

Afer Knife fish is a type of Knifefish and is not very common in the aquarium world. But due to its aggressive nature, this fish is fascinating for some. Afer Knife is the boldest Knifefish and is always ready to fight with its tank mates.

Afer Knife fish are usually found in central and western Africa and tend to live near the riverbed and search for food. Similarly, when you keep Afer Knife in an aquarium, they prefer dimly-lit areas covered with plants.

These fish are predatory in nature, so they do not work well with other fishes, even with their own species. When it comes to food, they prefer live food such as lance fish, earthworms, shrimps, and more. If you do not have live food available, you can also opt for frozen snacks or carnivorous pellets. Afer Knife fish tend to grow up to 20-30 inches, and the minimum tank requirement for their breeding is at least 200 gallons.

Afer Knife

Red Tail Shark

Red Tail Shark is a fish you may have seen before or even have owned before, but you may not know how to look after it properly. Red Tail Shark is not a true full grown shark, but it belongs to the same group as goldfish.

Even though most people confuse them with the Rainbow Shark, they are not the same. This fish is very attractive, with a black or gray-colored body and a vibrant red tail, which is how they got their name.

Young Red Tail Sharks have a timid personality and even hide from their tank mates. However, as they start to grow old, they become more mature and extremely territorial, which is also when their aggressiveness starts to show. They won’t usually attack other fish, but they will chase them relentlessly.

The best part about these fish is that they are omnivorous, so you won’t have any issue feeding them. You can give them shrimp, bloodworms, fruits, and even vegetables such as zucchini and cucumber. They even feed on tank algae!

Red Tail Shark

Ornate Bichir

Ornate Bichir is a unique species of aggressive freshwater fish and has been around for millions of years. These fish are still found in the northeastern areas of Africa, and they look like a mix of an eel and a fish.

Most people opt for these fish due to their large size because the Ornate Bichir can grow up to 2 feet long. The Bichir has a unique appearance as well, with a long and slender body and gorgeous triangular-looking fins.

The surprising part about this aggressive freshwater fish is that it has incredibly weak eyesight, so it relies on other senses to look for food. Moreover, Ornate Bichir can withstand different conditions with ease and are very tough.

The aggressiveness of this fish shows when it is kept with other tank mates. Its power move is to nip the tank mate’s fins as a way of attacking. When placed in an aquarium, you’ll find that they like to stay at the bottom. For this reason, make sure you fill it with good sand, because gravel sand can injure their bellies. Bichirs are also carnivorous, and if not given food on time they may feed on smaller tank mates.

Ornate Bichir

Tiger Barb

Don’t let their small size fool you! The Tiger Barb may be a maximum of 4 inches long, but it is one of the most aggressive freshwater fish. Many people underestimate the fish due to their vibrant color and size; however, you need to carefully pick their tank mates.

Tiger Barbs are aggressive towards their neighbors and do not do well in community tanks. These fish also terrorize their mates and chase them through the aquarium. But the good news is that if you keep 4-6 of them together, their aggressive behavior is toned down to a minimum.

Try to keep at least 6 Tiger Barbs to have a stunning display of color in your aquarium. The yellowish-orange color of these fish and the 4 vertical stripes give them a tiger-like look, hence the name Tiger Barb.

Tiger Barb


Severums are another type of aggressive freshwater fish and are found in South America. They are usually in the northern area and thrive in lakes and streams.

Severums are also called Banded Cichlids and have a very interesting appearance. Their shallow chin and strong forehead give them a rounded look. Male Severums have a distinctive mark on their head that makes them stand out.

Even though they classify as aggressive fish, they often do perfectly well in tanks and do not attack their tank mates as frequently as other aggressive fish. The surprising part about these fish is that they recognize their owner and even eat directly from their hand.

Severums can grow up to 8 inches, and need a tank of at least 55 gallons to grow properly. However, even though these fishes can live in a community, they get very protective during breeding and might even resort to aggression if need be. This is why you should move them to a separate tank for breeding, where they can look after their young ones and not have any territorial issues.


Convict Cichlid

These aggressive freshwater fish are one of the most popular Cichlid family species. They are gorgeous to look at, with a silvery gray color and vertical black stripes on top. Since these fish look similar to a prisoner’s uniform, they are named Convict.

Even though they grow to only 6 inches in length, these fish are extremely aggressive. In a community tank, you should keep Convict Cichlid with larger, equally aggressive fish because they will eat smaller tank mates right away.

They also need plenty of hiding places, so make sure you decorate the tank with caves, rocks, and driftwoods, so they can feel safe. With the help of these decorations, this fish will keep its aggression to a minimum.

Convict Cichlid

Pea Puffer

Pea Puffers are as cute as their name implies, but don’t let their appearance fool you. These fish are extremely aggressive, and they have no issue fighting with other fish. You can keep them with their own species but make sure that the tank is large enough for them to have their own space. Otherwise, Pea Puffer will not hesitate in fighting over territories.

Pea Puffers come from rivers in Southwest India, and in order for them to survive in an aquarium, you must match the living conditions of the river. Your tank must be well-decorated with plenty of hiding space such as caves or driftwood. Also, add in plants and vegetation so the fish can hide if it feels threatened.

This fish grows up to a maximum of 1.5 inches, so a 10-gallon tank will be good enough for them to swim around and live in. By nature, Pea Puffers are very curious, which is why they are bound to investigate every corner of your tank, so don’t be surprised if you catch them doing just that.

Pea Puffer

Bucktooth Tetra

Bucktooth Tetra is another very attractive fish and adds a pop of shimmer to the tank. It has a silvery gray color with a semi-transparent body, which makes its shiny portion stand out.

However, as gorgeous as they are, these fish are most comfortable in a single-species environment and are not very good when interacting with other species. They also have two large dots as their signature mark; one dot is at the base of the tail, whereas the other is on the middle of their body. Once you put them in a tank, you will notice a touch of yellow and red on their body as well.

As far as aggressiveness is concerned, these fish are known to rip off and eat the scales of other fishes. They even attack other tetras, which is why it is recommended that you keep them separate or in a group of 12 – the larger the group, the fewer the dominance issues.

Bucktooth Tetra

Jaguar Cichlid

One look at Jaguar Cichlid, and you will understand where the name comes from. This fish has black splotches all over it, making it resemble a jaguar. Interestingly enough, these fish do not look like this when they are small. As baby fish, Jaguar Cichlid have a silver and slight gold look with thick black stripes on their body. When they start to mature however, their appearance changes and their signature Jaguar-like spots appear.

These fish are very fierce predators and have easily extended jaws. Due to their predatory nature, they can swim extremely fast and are always ready to protect themselves.

Young Jaguar Cichlid can survive on flakes and pellets, but adult Cichlids need protein-packed dinners such as crickets, earthworms, and other small fish. Feeding them is a fascinating task because they prefer live food.

Jaguar Cichlid

Red Terror Cichlid

The Red Terror Cichlid is another extremely aggressive freshwater fish which grows up to be very large. The maximum size a fully adult male fish can reach is around 20 inches, whereas a female can reach up to 15 inches. There are very few species, such as Wolf Cichlid and Umber Cichlid, that are larger than the Red Terror Cichlid.

This fish is very colorful and vibrant, so it adds a pop of color to your tank. Male Cichlids have long fins, whereas females have a deep reddish-orange color. Due to their aggressive nature, you cannot keep them with other fish, especially after they mate.

Red Terror Cichlid can be very protective parents that can kill any fish present in the tank, regardless of its size. Sometimes, these fish can even nip at your fingers during feeding, so if you can provide them with enough space in the tank, you can keep them in the tank easily.

Red Terror Cichlid

Betta Fish

If you search for a gorgeous-looking fish for your tank, Betta Fish will be on the top of the search results. This fish is one of the most popular species for tanks and indoor aquariums. However, it is still an aggressive fish, so only experienced owners can keep it properly.

Bettas have a harsh personality, so they do not get along with their own species, let alone other fishes. They also like to stay alone, without any tank mates. This is why you can keep one or two Bettas in different habitats. However, if you do want to create a community tank with this gorgeous fish, there are a few fish species that Bettas can co-exist with. These include Catfish, Black Tetras, Poecilia, and Bloodfin Tetras.

As aggressive as this fish sounds, feeding it is not a very difficult task. You can buy flakes created for Betta Fish, and this is all they need for good and healthy growth. Since they are omnivores, you can also feed them certain plants if you want.

Betta Fish

Flowerhorn Cichlid

Flowerhorn Cichlid is another aggressive freshwater fish that originates from Southeast Asia. It is very easily distinguished due to its unique shape and bright red color. The distinguishing feature of this fish is its nuchal hump, which is very noticeable on the male Cichlid. Some other physical features of this fish include a lumpy chin, round bulging eyes, and exceedingly prominent lips. A bright pink or red color also covers the fish’s entire body, and dark black spots run all over it, giving it a unique detail.

Like other Cichlid species, flowerhorns are aggressive, so keeping them in separate tanks is a good idea. However, if you want to create a community for the fish, flowerhorns work well with Tiger Oscars, Jaguar Cichlids, Plecostomus, and Leopard Plecos.

They can also bite other fishes and even you if you are working in the tank, so it is essential that they have a lot of space to move around. Flowerhorns are omnivores and eat smaller fishes and plants, so if you find your aquarium’s plants missing, you know who to hold responsible!

Flowerhorn Cichlid


Oscar Fish is another stunning aggressive freshwater fish. This fish has orange and black splotches all over and can grow up to 12 inches in size. It can reach this length within 12 months, since they usually tend to grow one inch every month.

However, these fish are very aggressive, and do not prefer living with tank mates. The ideal living situation is to set up an aquarium filled with Oscar fish only, so that there are no issues. But if you do want to keep them with other fish, make sure you pick them wisely. Some species that go well with Oscar Fish include Arowanas, Silver Dollars, Jaguar Cichlids, and Green Terrors.

Oscar fish tend to grow quickly, so you must get a large tank of around 55 gallons to house them. Also, don’t forget to decorate the aquarium with caves, vegetation, and rocks.

Oscar fish

Aimara Wolf Fish

Even though this aggressive freshwater fish is not as expensive as Arowana, it can cost you a few hundred dollars. This fish is predatory in nature and has a very sharp and strong set of teeth that you do not want to mess with.

Aimara fish are four feet in length and are very fast swimmers, which is why you must provide them with a large tank and ample space to move around. They are hardy in nature and can adapt to the tank environment, but they are not very friendly tank mates.

Due to their aggressive nature, Aimara Wolf fish do not bond well with other fishes and can even attack them if they feel they need to. It is recommended that you keep these fish separate, and in a huge tank of around 300 gallons so that they can grow in peace.

The best part about this fish is that it is not a picky eater, and it can survive on live or frozen meaty food easily.

Aimara Wolf Fish

African Cichlid

If you are looking to add some vibrant color to your tank, consider getting the African Cichlid. These species are incredibly bright and colorful with their glowing yellow body and a touch of blue on their head. However, as beautiful as these fish look, they are quite aggressive, so they require special care.

These Cichlids can grow around 8 inches long and are extremely active in nature. They love to continuously swim around the tank, which makes them a sight for sore eyes. Plus, if these fish see you moving outside the tank, they think you are feeding them and will follow you around.

What is surprising is that African Cichlids like to move around so much that if someone tries to scare them, they will jump out of the tank!

You will have a fun time keeping these fish in your aquarium because they can live up to 15 years, and feeding them is fun too! Some Cichlids are omnivores, whereas some are carnivores, so make sure you figure that out before you get one for your tank. This way you will know whether you can keep them with other small fishes or not and what to feed them.

African Cichlid


What is the most aggressive type of freshwater fish?

The most aggressive type of freshwater fish is the Piranha. They have razor-sharp teeth and eat both meat and plants. They are very ferocious fishes and have an aggressive behavior towards other fish in the tank, which is why they are best kept alone.

What fish is territorial?

Cichlid fish is very territorial, and when it doesn’t get enough space for itself, it can end up harming other fish in the community. There are some peaceful cichlids as well, but they end up being aggressive when it comes to defending their eggs.

What is the most vicious freshwater fish?

Piranhas are considered the most feared and vicious freshwater fish present today. They move together in groups and can harm other fish easily if they are hungry.

Are Tetras aggressive fish?

Tetra fish are usually very peaceful and social, which allows them to be a part of a community tank easily. However, not all Tetra fishes are peaceful; some species can be very aggressive and will bite other long-finned fishes as a sign of attack. So make sure you choose the right species for your tank.

What are the hardiest freshwater fish?

When it comes to hardy freshwater fish, some examples include molly, guppy, platy, some tetras, and swordtail. Usually, fishes are hardy when they are bred in tanks from the start. Wild-caught fishes take a lot of time to adapt to captivity breeding. As a beginner, Danios is a great hardy freshwater fish that you can get for your tank.

Are Bettas aggressive?

Bettas may be gorgeous, but they are also exceptionally aggressive. They fight other fish and even with one another to death. Another name for Bettas is Siamese fighting fish, because of their aggressive nature.


There’s no doubt that aggressive fish add a lot of personality to your aquarium, but taking care of them is a demanding task. If you want to get these species for your tank, don’t shy away from doing some research first, because if their needs are not met, they can be a danger for the other fish in your aquarium.

So make sure you know all about the aggressive freshwater fish you’re planning to get and the kind of environment they prefer, so that you can personalize your tank according to their needs.