aggressive freshwater aquarium fish

Convict Cichlid

Fish kept in freshwater aquariums tend to be helpful neighbors. However, if not provided the proper conditions, the ones described below can be quite aggressive. Before introducing any species to your aquarium, it's critical to understand which ones will need to have the upper hand. Here are some examples of aggressive behavior to watch out for, as well as the fish that exhibit it the most frequently.

What Does Aggressive Behavior Look Like?

There are a few specific examples of what to look for if you think your aggressive fish is harassing other individuals in their tank.

Charging/Active Attacking

This conduct is simple to identify. The two fish charge each other and either headbutt or bite the other. Meeker fish may occasionally remain concealed for extended periods of time just due to the danger of an encounter.


In an aquarium, there is a lot of rivalry for food, breeding, or space. Fish that are aggressive may move quickly while consuming as much food as they can, taking it from the mouths and even the gills of other fish. Use your filter output or a powerhead to distribute a variety of floating and sinking foods around your tank to reduce food competition.


Depending on the species, some fish parents are relaxed while others would use all of their might to protect their unborn children. Give children lots of space since combative parents often band together to attack. Any human hands that approach their nest too closely will be attacked.

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    Freshwater angelfish

    These fish may coexist peacefully in a group as youngsters. But eventually, one member of the group will begin to pick on the others and will need to be expelled. Then another begins to act as the catalyst, followed by another, and so on until all of your angelfish are separated. Take additional care while handling any breeding fish since these fish are also very protective of their young. They have been known to bite the hands that feed them!

    Species Overview

    Length: Up to six inches

    Physical Characteristics: Black, white, and yellow marbled pattern; long and thin fins with delicate webbing

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    Jack Dempsey (Rocio octofasciatum)

    The Jack Dempsey is one of the Central American cichlid species and has several different hues. It is simple to think of these fish as being aggressive given their nickname in the popular boxing sport. Jack Dempseys are renowned for being ferocious redecorators, digging into their sandy tank bottoms to uproot plants and relocate smaller decor objects. Smaller fish should not be kept with them or they will be eaten. They need tanks with a bigger capacity.

    Species Overview

    Length: Up to ten inches

    Physical Characteristics: Strong facial features; large oval body with long fins

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    Convict Cichlid (Amatitlania nigrofasciata)

    Convict Cichlids come in several variations, including the Zebra, Black, and Pink. These cichlids, which are also a type from Central America, enjoy having lots of places to hide in their tank. They may be quite hostile against any smaller fish or larger, less aggressive fish, while only reaching a maximum length of around 6 inches. They will reproduce in pairs and equally distribute parenting responsibilities between the male and female.

    Species Overview

    Length: Up to six inches

    Physical Characteristics: Multiple black stripes running across the body; males have larger dorsal fins than females

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    Red Devil (Amphilophus labiatus)

    Another species of cichlid that is appropriately called for its aggressive nature is the Red Devil. These fish may reach a length of 15 inches, are ferocious diggers, and need 50 liters each. Because they have a reputation for toppling decorations, arrange any pebbles or branches carefully to prevent them from falling on your fish. Due to its intense aggression, the Red Devil can only be kept with a very small number of fish. Fish that are unable to protect themselves should not be added.

    This fish is commonly confused with the Midas Cichlid (Amphilophus citrinellus), who also is sometimes termed the Red Devil Cichlid.

    Species Overview

    Length: Up to 15 inches

    Physical Characteristics: Stocky with pointed fins; classic red color

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    Oscar (Astronotus ocellatus)

    Oscars come in a wide variety that may be bought. The Zebra, Tiger, Red, and Lemon are a few of the most popular. These fish have been developed over many generations to exhibit certain color patterns even though they are all the same species. These fish may be quite aggressive with the tank decorations but are only moderately hostile against other fish. Unpopular heaters have been reported to be smashed by some fish. These fish may become up to one foot long and need at least 70 liters of water each.

    It is suggested to keep Oscars in systems with a to reduce "decor aggressiveness." The number of components that must be stored in the main tank will be reduced as a result.

    Species Overview

    Length: Up to one foot

    Physical Characteristics: White with black, orange, and red outlines and spots

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    Bucktooth Tetra (Exodon paradoxus)

    Do not be misled by the word "tetra"! The Exodon Paradox, also known as the Bucktooth Tetra, is widely known for biting at its neighbors, in contrast to their laid-back tetra kin. They catch other fish and small insects with the help of their razor-sharp front incisors. It is advisable to keep these fish alongside other members of their own species. The ideal number is twelve or more to prevent conflict.

    Species Overview

    Length: Up to three inches

    Physical Characteristics: Bright, metallic silver body with yellow fins, sometimes with orange and red tips

Other fish species can also be violent or only mildly antagonistic. This list might be expanded to include many more cichlid species that are more uncommon. When you want to put an aggressive fish in your tank, keep the following things in mind:

  • Always add the most aggressive fish to your tank last. If they are to be added in a group, add the entire group together.
  • If you are not planning on breeding your fish, do not keep mating pairs together.
  • If you have room to make your tank bigger or make more hiding spots, do so prior to moving in the new aggressive roommate.
  • Limit competition during feeding time by feeding a varied water-column diet (sinking/floating/neutral) and spread it out using your filter outflow or a powerhead.