Are Plecos Aggressive?

Plecos are not aggressive. However, they can get aggressive for multiple reasons such as stress, illness, being underfed, or being overcrowded.

They can be pretty docile given that you consider and act on these factors.

Below you’ll find a full discussion on what makes plecos aggressive and what to do to prevent their aggressiveness.

Want to know more? Keep on reading.

Are Plecos Aggressive?

Plecos aren’t aggressive. However, we need to get deeper into the factors that might make them aggressive. To how they’re aggressive, and to how to prevent their aggressiveness.

Galaxy Pleco

What Makes Plecos Aggressive?

There are several reasons which can turn your otherwise peaceful plecos into aggressive fish terrorizing your tank.


Plecos can grow to be very large. Once mature, you have to put them in big tanks that would give them their own suitable space.

If short spaces restrict their natural movement, they may get aggressive. Also, if other fish approach their space due to overcrowding, plecos can get territorial.

Additionally, the lack of oxygen caused by overcrowding may make your plecos stressed.

Putting Multiple Plecos Together

Plecos can’t tolerate being put together in the same tank. Once they mature, they’ll tolerate each other less and less and you’ll have to separate them.

Male plecos can get highly territorial and attack each other for dominance. This can lead to violent fights that might leave your plecos severely injured.

Lack of Food

Plecos can become aggressive when they’re hungry or underfed.

Competition for food can lead to stress for your plecos.

If they’re fighting for food with other fish in the tank, then maybe the food is insufficient for all the fish.


Stress can be the main reason for your plecos becoming aggressive. This happens as a result of one or more of the following conditions:

  • Overcrowding
  • Lack of oxygen
  • Inadequate lighting
  • Poor water quality
  • High ammonia levels
  • Changes in water chemistry
  • Bullying from other fish

You’ll be able to spot signs that might indicate that they’re stressed. This includes:

  • Anxiety
  • Loss of appetite
  • Hiding
  • Swimming erratically
  • Hitting the glass walls
  • Lying motionless on the ground
  • Chasing and attacking other fish


Illness is another reason that could make your plecos stressed and aggressive. Signs that indicate their illness might be similar to those of being stressed.

To identify that the reason for stress is in fact illness you have to observe your fish’s behavior constantly. Common signs are:

  • Loss of appetite
  • Erratic movements
  • Dullness
  • Loss of color
  • Bloating

During Breeding

During breeding, plecos can become very aggressive, especially males.

After the male fertilizes the eggs, they start guarding them against other fish in the tank that may try to eat them. While guarding them, they can become highly territorial and protective of the eggs.

Close up of Pleco

Would Plecos Attack Each Other?

Plecos are very territorial and would fight each other if put together. Male plecos may even fight each other over the right to mate with a certain female.

Forms of fighting could be:

  • Chasing
  • Biting
  • Nipping at each other

Would Plecos Attack Other Fish?

Usually, plecos co-exist with other fish peacefully without fighting or attacking.

They dwell at the bottom while other fish can occupy the middle and the upper layers, without any interference possible.

However, they might fight only in the case of self-defense or if they’re protecting their eggs.

Would Plecos Harm Other Fish?

Plecos have a weird tendency to attach themselves or even suck on surfaces. They’d do that to both hard surfaces and large slow-moving fish.

They’d suck on fish such as goldfish leading to open sores on goldfish’s skin. Sores that might lead to bacterial infections and even diseases.

They can also nip the fins of fish such as angelfish and injure them.

Would Plecos Eat Other Fish?

Plecos are omnivorous, which means that they can eat whatever they can, either plant-based or animal-based. However, they don’t usually eat other fish.

They might eat small fish, but most of the time they eat dead fish or dying fish that sinks to the bottom.

Do Plecos Bite?

Plecos have teeth and can bite. Though usually, they won’t bite.

They only bite in case of self-defense or during the breeding season if another fish is trying to eat their eggs.

They may bite other fish to scare them away, but most of the time, they choose to hide or swim away.

How to Prevent Plecos From Becoming Aggressive?

To prevent plecos’ aggressiveness, first, you have to understand the reason behind their attitude, and then treat it accordingly.

Below, you’ll find some of the most useful tips to prevent their aggressiveness.

Use Large Tanks

Plecos can grow to be very large. Provide them with large aquariums that could facilitate moving around freely.

Additionally, they don’t like to share space and wouldn’t like other fish to invade their territory. So, make sure the tank is big enough for everyone.

Make the Aquarium a Suitable Home

Fill the tank with fish that are compatible with plecos. So plecos won’t get hurt, or hurt other fish.

Provide them with hiding places. You can add rocks, plants, caves, and wood parts that can act as shelters for when they feel threatened.

Avoid putting more than one pleco in your aquarium to reduce competition. However, there are exceptions such as the following:

  • When they’re breeding, you can put a male and a female together
  • When the eggs hatch and you have plenty of young plecos, you can put them together until they mature

Take Special Care of Your Plecos

Plecos grow with big appetites. Feed them properly to contain their aggression.

Check the water parameters regularly to prevent any sudden change that might upset them.

Always check them to see if they have any abnormal symptoms that might indicate sickness. If you observe anything unusual, contact your vet.

Final Thoughts

Are plecos aggressive? No, plecos are very peaceful fish that would just coexist with your other fish at the bottom of your aquarium.

However, If underfed, stressed, sick, or put with another pleco in the same tank, they might get aggressive and territorial.

Always, give your plecos space and make sure they’re healthy and properly fed.

Additionally, pay extra care as to which fish to put with your plecos in the same aquarium. Thus, neither type would get hurt.