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15 Predatory and Aggressive Aquarium Fish That Eat Other Fish

Eric is an aquarium enthusiast with over two decades of experience caring for a wide array of tropical fish.

Your aquarium setup went flawlessly. You chose the perfect spot in your home, the decorations looked fantastic, and you stocked it with a bunch of gorgeous freshwater fish. Beaming with pride, you rested your head on your pillow that night and counted guppies until you drifted blissfully into a sweet sleep.

But the next morning something seemed off. You were sure you’d stocked ten neon tetras, but now you only see eight. You must have miscounted.

When on the third morning you found only five neons, it slowly dawned on you. There was a murderer in your midst. One of your beautiful fish was snacking on your other beautiful fish!

How and why did this happen?

Why Do Aquarium Fish Eat Other Fish?

Big fish eat little fish. Some fish are predatory and will stalk and eat other fish. Others are opportunistic, and if we stock them with very small fish, they may eat them. Still others are simply too aggressive or territorial to keep with most tank mates, and they may kill them.

It should go without saying that you don’t want to mix predatory fish and fish that are easily preyed upon such as small tetras. You also want to make sure you don’t stock tiny fish with others who might grow large enough to eat them.

As I always mention in these articles, the most important thing is to research a fish before you bring it home so you better understand its behaviors. While that won't completely eliminate any surprises, it gives you the best chance of success.

List of Predatory and Aggressive Tropical Fish

Here are some of the aggressive fish you might encounter in the aquarium trade:

  1. Angelfish
  2. Leopard Bush Fish
  3. Oscar
  4. Bichir
  5. Green Spotted Puffer
  6. Red Devil
  7. Jack Dempsey
  8. Jaguar
  9. Texas Cichlid
  10. Red Terror
  11. Flowerhorn (hybrid cichlid)
  12. Peacock bass
  13. Red tail / rainbow shark
  14. Betta fish
  15. Gourami

Most novice and intermediate fish keepers aren’t going to bring home an Arowana, but they might make the mistake of stocking one of these fish without realizing the true nature of their new pet.

Read on to learn more about some of the common aggressive fish aquarium owners often regret bringing home.

Angelfish

Freshwater angelfish are among the most popular aquarium fish in the world, and probably among the most misunderstood. They are often kept in community tanks with smaller fish, and when they are juveniles, there are usually no problems.

However, they are aggressive ambush predators, and when they get a little bigger, you might notice some of your smaller fish have gone missing. You’ll want to avoid stocking angelfish with neons and other small tetras.

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Read More From Pethelpful

Angelfish have some care needs slightly beyond the average beginner, yet they are sold to novices every day across the world. Behavioral tendencies, tank mate compatibility, tank size, and predatory instincts are complex issues often overlooked by fish keepers who don’t know any better.

Angels are considered semi-aggressive fish, but they can also be quite aggressive in certain situations. Make sure you know what you are getting yourself into before you bring one home.

Leopard Bush Fish

Also called the spotted ctenopoma, spotted climbing perch, leopard gourami, African bush fish, or African leaf fish. They are anabantids, relatives of betta fish and gourami, and they are stealthy ambush predators. They do best in tanks with large, live plants, where they can blend in and wait for some unsuspecting snack to swim by.

While they are predators, when they aren’t hunting, they are quite docile fish and prone to bullying by other large, aggressive fish. They grow to about six inches long and can fit fish around half their size in their enormous mouths, so stock them with peaceful fish their size or bigger.

Better still, you might keep a single fish alone in a 55-gallon tank and feed live fish. They can live up to 10 years.

Green Spotted Puffer

Green Spotted Puffer

Green Spotted Puffer

Green spotted puffers can live in freshwater as juveniles but must acclimate to brackish water as they age. Still, I have seen pet stores list them as freshwater fish that “may nip fins.” If you bring one home and plop it into your pretty community aquarium, you will have a big surprise in the future.

The GSP is one of my favorite fish and, when you can do it correctly, they are a joy to keep. They are adorable as juveniles, but even then they are little wrecking machines that may attack, kill, and even eat any other fish in the tank.

They are best kept in single-specimen, specialized setups with specialized foods. That means a brackish tank and shelled foods such as pond snails. Unless you are willing to go all in, you should avoid this fish.

Oscar

Oscars are large, aggressive South American cichlids. While they may do okay with other fish when they are young, as adults they need proper setup and food. This means a tank of at least 55 gallons for a single fish, but bigger is better.

You can feed pellets as the main staple of their diet, but many oscar keepers prefer to include live foods in the form of feeder fish. This better mimics their natural diet of small fish and insects. For this reason, it ought to be obvious why you wouldn’t want to include small tropical fish as tank mates for an oscar.

Better tank mates include other large cichlids, provided you have a big enough tank, and large schooling fish such as silver dollars. However, if you are not an experienced fish keeper, you are probably better off keeping an oscar as a single fish or avoiding them altogether.

New World Cichlids

Along with the oscar and angelfish, there is a long list of new-world cichlids that can and will eat other fish in your tank. They are predators, but in the right setup, they can be wonderful fish to keep. This often means they should be kept in very large tanks, alone or with other large tank mates they can’t push around.

Here is a partial list of aggressive new-world cichlids:

  • Red Devil
  • Jack Dempsey
  • Jaguar
  • Texas Cichlid
  • Red Terror
  • Flowerhorn (hybrid)
  • Peacock bass

Once more, I will say, it is very important to research fish before you bring them home. They sell most of these fish as three or four-inch juveniles just trying to get by in the world, but as they get bigger and their natural instincts emerge, they can be a handful.

Carnivorous Fish FAQs

Here are a few things people wonder about when it comes to fish that eat other fish:

Do most fish eat other fish?

While not all fish are predatory, many are opportunistic feeders or browsers that will take advantage of a meal if it swims by. Doing the research before you bring a fish home and not mixing large fish with small fish can help avoid disaster.

What is the most aggressive tropical fish?

African cichlids are some of the most colorful freshwater fish you are going to find, known for their aggression and territorial behaviors. However, you should stock new-world cichlids with care as well. Many species are extremely aggressive and will not tolerate tank mates. A predator tank is in many ways the complete opposite of a community tank, but the same rules apply. You always want to stock fish that are compatible with each other.

Are betta fish predators?

Betta fish are known as aggressive fish, but when it comes to other fish, this is because of territorial and mating behaviors. While they may attempt to prey on snails or shrimp, and will not pass up very tiny fish such as fry if they can catch them, they won’t hunt other fish for food.

Are goldfish aggressive?

Goldfish are not tropical fish, but they often end up in tropical tanks managed by novices. They are not aggressive, but there are many reasons you don’t want to mix goldfish and tropical fish. One is because goldfish grow much larger than people expect, which means big goldfish can eat small fish if given the opportunity. Goldfish also pollute tanks quickly, and they require cooler water than tropical fish.

Betta fish won't prey on other fish, but they can be aggressive.

Betta fish won't prey on other fish, but they can be aggressive.

Should You Stock Fish That Eat Other Fish?

Aside from legal limitations, there isn’t a fish in the world you can’t stock if you have the experience and the right setup. But that is where the problem lies. Experienced fish keepers know what they are doing. They know how to keep aggressive fish in the right situation, and when they should avoid a fish if they can’t properly care for it.

On the other hand, novices are often blindsided by behaviors they weren't expecting, or the staff at the pet store never warned them about.

Again, therefore, it is so important to research fish before you bring them home.

Many experienced fishkeepers find great satisfaction in caring for predatory fish. They are a little more interactive than the typical community tank because of the feeding requirements, and maybe they have a little more personality.

It is up to you. The bottom line is to house whatever fish you stock in the correct tank with the right tank mates.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

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