Aquarium Fish Get Mean, Meet the Bad Guys

Red-bellied Piranha, Pygocentrus nattereriRed-bellied Piranha. Photo © Animal-World: Courtesy Jonas Hansel

Bad guys come in all shapes and sizes. Sometime even fish that are considered great community members can get mean!

There are several aquarium fish species which are known to exhibit aggressive behavior. One of the important causes of aggressive behavior inside the tank is attributed to their being territorial, thus you may find some fish species that chase away or nip at others as a means of protecting their space inside the tank.

Yet fish aggressiveness is also attributed to competition for food and difference in size. Sometimes fish will fight when a dominant one feels that its status is being threatened by another fish. Aggression can also be a warning sign; sick fish can become aggressive while other fish tend to bully sick fish. In some instances, a recognized peaceful fish can become aggressive, thus it is common to have one mean fish in the bunch.

The most common manifestations of aggression inside the tank include tail beating, fin-nipping, pushing water at the enemy, mouth-locked wresting, chasing, biting, and even killing.

When choosing to keep a community aquarium, you should know which species can live harmoniously together. Most species of aggressive fish are more suitable for a single species aquarium.

Some of the aggressive fish groups include the following:

Tiger Barb – The Tiger Barb is considered a good community fish however it is prone to nipping fins, thus they should not be kept with long-finned fish species such as angelfish. Tiger barbs can become aggressive if there is overcrowding inside the tank.

Large Tetras – Tetras are considered community dwellers however there may be an aggressive one in the group. When adding new fish, be sure to observe the temperament and whether the new addition is compatible with the rest of the inhabitants of the tank.

Cichlids – Many varieties of cichlids are aggressive and are best kept in one-species tank. Many cichlids can grow to very large sizes. These include the Green Terror, Jewel Cichlid, and Red or Tiger Oscar. African Cichlids are known to be highly predatory and extremely territorial. While not all Cichlids are very aggressive, the largest is usually the dominant one, behaving aggressively towards all the other tank inhabitants.

Giant Danio – The Giant Danio’s long and narrow body can crowd out other fish in the tank. It is also very active and likes to school.

Red Belly Piranha – Piranhas are notoriously predatory. They are known to eat live food. In fact, they will bite fingers when aggravated or hungry.

Large Gouramis – Kissing Gouramis are recognized for being mean and energetic. Gouramis are also considered fin nippers.

Large Rainbow Fish – Although Rainbow fish can live well with other species in a community tank, they can grow large and their fast speed makes it easier for them to prey on smaller inhabitants of the tank.

Wolf Fish – The freshwater wolf fish is a well-known aggressive predator. Also called “Piranha eater”, they have voracious appetites for feeder fish. Any fish that looks like prey can be disemboweled by the wolf fish. Although they don’t really mess with other fish, they are territorial and will nip other inhabitants of the tank.

Peter Hartono is the founder and CEO of Just Aquatic – a proud Australian company that provides excellent online aquarium supplies for betta fish tanks, goldfish tanks and also aquatic plant care products carrying top of the line brands including API, biOrb and Exo Terra.