Cardinal Tetras swimming in aquarium

Are Cardinal Tetras Aggressive?

The cardinal tetra is a fish from the freshwater rivers of Negro and Orinoco in the South America. It has a maximum length of 1.2 inches or about three centimeters. The most recognizable aspect of cardinal tetra a florescent blue line right in the middle of its body. The part of the body below this blue line is red in color.

The cardinal tetra closely resembles its cousin, the neon tetra.

A popular fish for aquariums

The cardinal tetra is very popular among fish lovers and aquarium keepers. It was very difficult to breed this fish until recently. Novel breeding techniques have allowed for more production.

For most people, keeping and maintaining an aquarium is a serious job. They take their fish very seriously. Aggressive fish is never the first choice for any fish lover since it may bring harm to itself and all the other fish within an aquarium. In the article below, we will discuss if the Cardinal Tetra is an aggressive breed, and what can be done about it.

How Cardinal Tetra behaves

It is always good to see this fish with its florescent glow gliding slowly within the peaceful waters of your aquarium. The striking color combination of the fish makes your wonder about its beauty and agility.

Cardinal Tetra is a peaceful creature and non-aggressive nature. It is usually found in groups and does not seem to have any problems with other fish.

Are Cardinal Tetras Aggressive?

Cardinal tetra is peaceful by natures but it may show aggression sometimes under specific circumstances like when it is feeding or mating. If your aquarium is small in size with more numbers of tetras, they might start showing aggressive behavior.

Another peculiar aspect of the cardinal tetra is that it marks its territory and guards it against invaders. Unwanted incursions may also lead to aggressive behavior.

Is Aggression Contagious in Tetras?

When a cardinal tetra becomes aggressive for any reason, it starts attacking its peers. Under such circumstance, a peaceful tetra which is attacked by an aggressive one becomes aggressive as well. This leads to fights.

Cardinal tetra likes living in groups so when you keep a single tetra within your aquarium, it will start getting stressed. This will lead towards aggression. The best way of solving this problem is to get a few more tetras so that they can give each other company.

Is your Cardinal Tetra Really Aggressive?

Sometimes, when you see a group of tetras fighting within the fish tank, they may not be fighting at all. Rather, they might be playing – chasing each other and nipping here and there. In fact, nipping the fin is usually perceived as violence but this is one of the ways tetras play with each other. This is normal behavior that must not be misunderstood for aggression.

Mating or fighting

For a new person who has just obtained a bunch of tetras, even mating would seem like fighting. The best way of avoiding this kind of fighting is to separate a pair of male and female tetra, and put them into another tank.


If your cardinal tetra is showing aggressive behavior, there is some reason behind it. The best option for you is to try and seek out that reason, and then get rid of it.

As a fish keeper, you should also do some research, and try to provide the best conditions for your tetras so that they can thrive peacefully.

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