Aggressive Freshwater Fish: 21 Loveable Rouges For Your Aquarium

Predatory aggressive freshwater fish are a fierce as they are stunning.

There’s a reason why, myself and countless others have adored owning predator tanks over the decades. They’re tons of fun to interactive with.

But you’ll have to make sure that you can accommodate their needs before you bring any of these carnivorous fish.

In this guide, I’ll share the best aggressive freshwater fish, including serval I have owned (and still do) over the decades, and go over the kind of attention they require.

1. Red-Bellied Piranha

  • Minimum tank size: 100 gallon (379 liter)
  • Maximum length: 1 foot (30 centimeters)

There’s no more iconic aggressive fish than red-bellied piranhas. These freshwater bad boys travel in large schools and can pick clean a large fish in minutes. They’re not quite the fearsome movie monsters that Hollywood makes them out to be, but they’re close enough that I wouldn’t stick my hand in the tank.

Pro tip: Piranhas are illegal in many states/provinces. Please, be sure of the laws in your area before you buy a piranha from some shady guy on Craigslist.

2. Jewel Cichlid

  • Minimum tank size: 30 gallon (113 liter)
  • Maximum length: 5.5 inches (14 centimeters)

This species is truly beautiful, especially when spawning. They’re also, pound for pound, one the most aggressive fish I have ever seen! You can find stories all over the internet about jewel cichlids harassing and killing fish 4 times their size. Definitely, keep them in a species only tank. If they pair up, they likely will not tolerate any other fish in the tank.

3. Giant Gourami

  • Minimum tank size: 250 gallon (950 liter)
  • Maximum length: 28 inches (70 centimeters)

They’re really not kidding when they call this fish “giant.” This is one of the biggest, and meanest, aquarium fish out there. Sometimes, you can keep this species with other large aquarium fish, but if the gourami starts to feel cramped for space, it could turn into Thunderdome in there. Giant gourami are an extremely valuable food fish in Southeast Asia. 

4. Flowerhorn Cichlid

Flowerhorn cichlid swimming alone
  • Minimum tank size: 75 gallon (284 liter)
  • Maximum length: 8-19 inches (20-48 centimeters)

The flowerhorn may not get as large as a giant gourami, and may not have the giant teeth of a piranha, but it makes up for that with pure unadulterated aggression. Males especially have a mean streak a mile wide. But fishkeepers just can’t resist the bright colors and those insane nuchal humps on the males. 

Related: Best Food For Flowerhorn Cichlids Compared & Reviewed

5. Jaguar Cichlid

  • Minimum tank size: 110 gallon (416 liter)
  • Maximum length: 18 inches (46 centimeters)

No doubt, this is a gorgeous fish. With an intricate pattern of spots and a mean attitude that is reminiscent of the big cat this fish is named for, you can’t help but be impressed by this species. This fish gets huge and doesn’t play well with others. Your only hope of having a tank mate is usually to put a male and female of the same size together and hope they pair off. 

6. Jack Dempsey Cichlid

Jack Dempsey fish
  • Minimum tank size: 55 gallon (208 liter)
  • Maximum length: 8-12 inches (20-30 centimeters)

I love Jack Dempseys. Although they can be territorial and quite aggressive sometimes, they can also be shy and retiring. I’ve always really enjoyed their colors. Against a dark substrate, their base color will be close to black and covered with iridescent speckles with a metallic sheen. On a lighter background, their base color is much lighter, almost pink.

7. Red Devil Cichlid

  • Minimum tank size: 75 gallon (284 liter)
  • Maximum length: 15 inches (38 centimeters)

Red devil cichlids are very active, “in your face” aggressive fish. But, all that energy can cause this species to be kind of destructive. They are notorious for shredding plants and rearranging the tank decor. I’ve heard of them knocking over rock work so it’s recommended to anchor pieces together with epoxy to secure them. However, these fish also have a lot of personality, which makes them a favorite with monster fish keepers. They love to come to the front of the tank when they see people to beg for a treat. 

8. Asian Arowana

Asian arowana (Scleropages formosus). Freshwater fish.
  • Minimum tank size: 110 gallon (416 liter)
  • Maximum length: 35 inches (90 centimeters)

Asian arowanas are simply stunning. With those red scales, and their imposing size, you can’t help but be drawn to them. They can be kept with other similar fish, like other arowanas or knifefish, but all tank mates need to be of a similar size. And war might still break out over territory or food in the tank. But, if you’ve got the room, there is nothing as impressive as a bright red arowana.

9. Wolf Cichlid

  • Minimum tank size: 300 gallon (1350 liters)
  • Maximum length: 28 inches (70 centimeters)

This behemoth is the largest on my list, males easily reach 2 feet in length and are very thick bodied fish. This bad boy even has teeth that stick out of its mouth that look like fangs. They’re absolutely gorgeous to look at, and are a very interactive fish, but they will happily murder any other fish you put in the tank.

10. Betta (aka Siamese Fighting Fish)

  • Minimum tank size: 5 gallon (19 liter)
  • Maximum length: 4 inches (10 centimeters)

It’s not too surprising that the species called a “Siamese fighting fish” can be pretty aggressive from time to time. You never know what you’re going to get with Bettas. Maybe you’ll come home with the chillest Betta that ever lived that will be nice to everybody. Or… you might get one that is so homicidal that it will attack anything that moves.

Males are the most aggressive but female bettas can also be fierce bullies, sometimes even killing each other. Always err on the side of caution with Bettas and have a plan in case you need to move the Betta or its tank mates to another aquarium. Males will fight with each other, or even other species of fish that resemble Bettas, like dwarf gouramis.

11. Rainbow Shark

Rainbow shark swimming in planted aquarium
  • Minimum tank size: 40 gallon (151 liter)
  • Maximum length: 6 inches (15 centimeters)

Again, some folks might be surprised to see this species on the list, but that just means they’ve never owned one of these fish. I have a motley crew of mean cichlids in one of my tanks. These guys are all rescues that got kicked out of other people’s tanks for being bullies.

My rainbow shark was so mean, I had to put him in that tank. At first, he was really timid. Now, he’ll chase and harass fish that outweigh him by a couple of pounds. Seriously, don’t underestimate this fish. And do not try to keep more than one in a tank. They will also fight ferociously with similar species, like the red tail shark. 

12. Red Tail Shark

  • Minimum tank size: 40 gallon (151 liter)
  • Maximum length: 6 inches (15 centimeters) 

Like its close cousin the rainbow shark, the red tail shark is another fiercely territorial bottom feeder. This species is very assertive and will chase, harass and bite other fish that wander near. Don’t be fooled by the cute looks, these guys can be super mean. They are much too aggressive to be mixed with more timid bottom feeders like corydoras catfish.

13. Oscar

Oscar fish (Astronotus ocellatus), closeup shot swimming in aquarium
  • Minimum tank size: 75 gallon (284 liter)
  • Maximum length: 14 inches (36 centimeters)

This popular giant of a fish has a great personality when it comes to humans. They readily come up to the front of the tank to beg for food. But, when it comes to other fish, they can be merciless bullies.

Oscars will definitely gulp down any fish small enough to fit in their mouths. Even fish that are too big for them to swallow may be chased, rammed and bitten until they get so stressed they die. This species needs to be kept with other large, aggressive fish to keep them in check. They’ll do best with fish that were raised up with them, but even then, there could be fights over territory. 

14. Convict Cichlid

  • Minimum tank size: 40 gallon (151 liter)
  • Maximum length: 6 inches (15 centimeters)

This Central American fish is popular with aquarists due to its striking pattern of black stripes on gray-blue background. Convicts aren’t giants like a piranha or red devil, but don’t be fooled by their small size.

This is a fierce, fierce fish, especially when spawning. When they are defending their territory, a pair of convicts will drive all the other fish away and nip at much larger fish until they die. Do not ever try to keep this species in a regular community tank, they’ll decimate the other fish.

15. Bumblebee Cichlid

  • Minimum tank size: 75 gallon (284 liter)
  • Maximum length: 6 inches (15 centimeters)

This is another striking fish with a seriously bad attitude. They display a bright yellow base color with dark brown vertical striping. Males are a bit brighter than females. But, bumblebees carry a sting. I’ve kept two over the years and they were by far the meanest of all the Mbuna cichlids I kept. So, great looking fish, but it may destroy every tank mate it comes across.

16. Green Severum 

  • Minimum tank size: 55 gallon (208 liter)
  • Maximum length: 10 inches (25 centimeters)

OK it might surprise some people to see the severum listed here because they’re often tagged as “semi-aggressive.” I have to totally disagree with this listing. I’ve owned several severums over the years and have found them to be meaner and bossier than even Jack Dempsey’s.

I had a murderous female that would destroy any other fish in the tank and would even attack the bubbles from the airstone and the intake tube of the filter. She also frequently attacked us and/or the gravel vacuum when we were performing water changes.

Severums will often rush to the front of the tank if your face gets too close and try to bite you through the glass. Plain and simple, they’re mean, they’ll shred any live plant you put in the tank and they’ll sometimes bully other fish in the tank, sometimes to death. But, if you like a feisty fish, you’ll love their spunk and personality.

17. Freshwater Pufferfish

  • Minimum tank size: 30 gallon (113 liter)
  • Maximum length: species dependent

I wanted to add pufferfish to this list because people are often surprised by how evil these adorable little guys really are. Despite their comical appearance, pufferfish have a nasty bite. They have a hard beak for a mouth that can take chunks out of any fish they come across. Don’t be fooled by how cute they are! They love to bumble around and nip the fins of any tank mate that comes near them. Keep pufferfish in a species only tank.

Pro Tip: Some species of pufferfish actually need brackish water but are irresponsibly held and sold as a freshwater fish. Please, research the individual species before you buy a pufferfish.

18. Kenyi Cichlid

  • Minimum tank size: 55 gallon (208 liter)
  • Maximum length: 4-6 inches (10-15 centimeters)

Kenyi cichlids are a gorgeous, yet ferocious, Mbuna cichlid from Lake Malawi. As juveniles, males and females exhibit the same blue color with dark vertical stripes. Once fully mature, males will be a brilliant yellow color and females will remain blue. These guys are fast and vicious. They will attack other species that have similar colors/patterns.

19. Acei Cichlid

Katherine’s own Acei Cichlid
  • Minimum tank size: 55 gallon (208 liter)
  • Maximum length: 6 inches (15 centimeters)

This is another species that is only listed as “semi-aggressive,” but I really have to disagree. I’ve owned several Acei cichlids and have found them to be pretty challenging. They’re super quick and will chase and nip all day. Luckily, they don’t get as huge as something like a wolf cichlid, but for their size they can really wreak some havoc.

20. Texas Cichlid

Katherine’s own Texas Cichlid, Dallas
  • Minimum tank size: 55 gallon (208 liter) 
  • Maximum length: 12 inches (30 centimeters)

I love this species. I’ve kept one for several years now, his name is Dallas, and he’s a total jerk. He will bully fish twice his size. Texas cichlids are the only species of cichlid native to the United States. They truly are beautiful, mine is a ham who poses for pictures, but believe me, they pack a serious punch. Dallas is definitely the tank boss and will hand out a beating to anyone who tries to challenge him.

21. Green Terror

Green terror cichlid swimming over rock
  • Minimum tank size: 75 gallon (284 liter)
  • Maximum length: 10 inches (25 centimeters)

The final species I’ll cover is the aptly named green terror. OK there are lots of pretty fish on this list, but the green terror is a whole other level. They’re a beige-ish color that’s overlaid by rows of blue-green, iridescent speckles.

They also have large showy fins trimmed with bright orange. This is a super bossy fish that swims around the tank and will chase any fish it comes across. Not at all a shy or retiring fish, green terrors boldly charge through the tank, strutting their strength.

Which Aggressive Freshwater Fish Do You Want?

Why do we love aggressive fish?

I guess it’s interesting that something so pretty can also be so tough and assertive. They’re not just fun to look at, they can actually throw their weight around.

There are some real beauties on this list, but you have to make sure that you can accommodate their needs before you bring any of them home. 

I can’t emphasize enough how important it is to research a fish species before you decide to buy it. Definitely check how big it gets and how large of a tank you’re going to need.

I will say, having owned several of the fish on this list, these aggressive bruisers usually have a ton of personality and really make great pets.

These species tend to be more intelligent and interact with their owners a great deal.

I hope you find this information helpful.

I wish you and your fish the very best!

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Katherine Morgan
Hey, there! I'm Katherine from Northwest Florida. A nunchuck specialist, I've kept aquariums for over two decades, enjoy experimenting with low-tech planted setups and an avid South American cichlid enthusiast. If You'd like to see more of my tanks, check out my Instagram

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