In this guide, we are going to be discussing fish aggression and how it can happen even in peaceful community aquariums.

In this guide we are going to discuss the following bullet points:

  • Not all fish are peaceful.
  • Each fish has its own personality.
  • Some “peaceful” fish can be aggressive.


Not all fish are peaceful

It’s pretty common knowledge when you’re shopping for fish that not all fish can get along. When you go to a fish store, they will have fish separated in aggressive tanks versus community/peaceful tanks. If you’re unsure about a particular fish temperament, you can always ask the store employees. Some fish that are labeled as peaceful can still get aggressive. For example, certain Mollies will get aggressive for no real reason. I have noticed this with Sailfin Mollies the most. Each fish will have its own personality. So be prepared to have fish that don’t get along. It’s not super common, but it’s common enough to be aware of.

Understanding Fish Aggression

Each fish have their own personality

Like I stated in the previous paragraph, each fish can have its own personality no matter what kind of species it is. For example, some fish will be shy and timid while others will be friendly and interact with you. For example, most of my guppies are very friendly and always come to the front of the aquarium whenever I’m around even if they’re not hungry. No matter what they want to interact with me. Some of my fish like my catfish are quite the opposite. They don’t like me looking into the tank, however when I stick my hand in there to do maintenance that’s when they run. Also, Pleco is very shy and tries to avoid me.

Sail fin Molly

Some peaceful fish can be aggressive

All fish will become slightly aggressive during breeding. There are a few rules to this example. For example, male guppies will relentlessly chase females in order to impregnate them. The same behavior is common with Cory Cats. Some fish such as a Pleco will breed together, and then the male will guard the eggs very aggressively against other fish, even though a Pleco is considered a peaceful fish.


I’d like to wrap this post up by saying that you need to be aware of individual fish personalities before purchasing fish. Just in case you’re buying fish for say a small child, it would not be good for a child to see their fish fighting. Also be sure not to mix fish that are aggressive and nonaggressive, if you’re unsure on the fish temperament be sure to ask a store employee at your local fish store.


Also be sure to check our homepage on a regular basis as we plan on releasing more detailed posts on performing maintenance on your tanks, understanding fish aggression, fish breeding, clear water tips, and product reviews. View our guides section here.