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Can You Keep A Green Terror With An Oscar?

Keeping larger fish in aquariums is becoming increasingly popular again so species like the green terror and oscar are increasing in popularity again.

After publishing our green terror and jack dempsey comparison article a couple of days ago, we noticed a number of people asking other questions about keeping green terrors.

One of the more common questions that we have seen other people asking about recently is about keeping a green terror with an oscar so we wanted to cover this in its own dedicated article.

Now, we know that the default, standard advice that you will get from a local fish store or on social media is not to keep the two together but in the right setup, the two can work well.

Will Green Terrors And Oscars Be Aggressive To Each Other?

Both green terrors and oscars can be aggressive fish if their tank setups are not optimal. This means that keeping both fish species in the same tank has a high chance of aggression breaking out between the fish.

Not only can fin nipping, chasing, and full blown fights between a green terror and an oscar in the same tank be common but one fish can end up getting injured or even dying.

The green terror will usually beat the oscar even if it is smaller at the time of the fight. We have seen a number of people on social media reporting that they added a young green terror to their tank with an oscar and the green terror ended up killing their adult, fully grown oscar.

Can You Put Green Terrors With Oscars?

If you plan everything out and have the required budget to keep a suitable aquarium tank for your green terror and oscar in the same tank then it can be done with aggression being kept to an absolute minimum.

Now, before we go any further, we just want to say that this will not be cheap and ideally, you will already have at least a years worth of fish keeping experience, ideally involving aggressive fish species.

If these two points are met then you can definitely keep green terrors with oscars in the same aquarium with minimal issues.

What Size Aquarium Tank Do I Need To Keep A Green Terror And Oscar?

The most common reason that green terrors and oscars in the same tank fish is due to a lack of available space. Even experienced fish keepers make the mistake of keeping their fish in a small tank resulting in the two fishing each other.

We will be offering some general advice on tank sizes now but you have to keep in mind that our suggestions are the MINIMUM tank size, not the optimal tank size. If you have the budget available then you should always go with a larger tank if possible when looking to keep green terrors and oscars in the same tank.

If you are getting your green terror and oscar as baby fish then you are able to start them off in a 50 gallon aquarium tank. Just keep in mind that both fish species can grow quickly and as they grow, they will need to be moved to larger aquarium setups.

Due to this, many people will just skill a dedicated tank for the fish when they are young and just purchase the larger tank for their expected adult sizes for the green terror and oscar to grow into.

Both oscars and green terrors can end up being between eight and twelve inches long when fully grown so they definitely need a large aquarium when they are adults.

Most people should be getting a 100 gallon long tank for any setup that has a green terror and an oscar in the same tank but the larger the tank the better.

Please not that this is specifically just for a green terror and an oscar, if you want additional fish in there, even small bottom feeders then the tank should be larger if possible.

When Should I Add Both Of The Fish To The Tank?

It is usually better to add your green terror and oscar to the tank at the same time when they are young. This allows them to grow up with each other in the tank and be used to each other’s presence from a young age.

If you add the fish at different times then the fish that has been in the tank the longest may view the tank as its territory and attack the newer fish causing aggression between the two that can sometimes last until one fish is dead.

That said, some people have been able to add a green terror or an oscar to a tank that has had the other species in it for years with minimal issues. Just keep in mind that there will be a higher than average chance of aggression between the two in this situation.

Do I Need To Add Hides To The Tank?

You are going to need to provide hiding places for both of your fish no matter what size tank you have or how many fish you have in the tank.

The reason for this is that aggressive fish subdue their aggression when they cannot see each other. If two potentially aggressive fish species can see each other then they are more likely to attack each.

The issue with green terrors and oscars is that when fully grown, they are far too large for the traditional fish hides available on the market.

One quick and easy work around for this that many people who keep green terrors or oscars in their tanks, even if they are in separate tanks is to take advantage of aquarium safe terracotta pots.

We have a dedicated article going over using terracotta pots in your aquarium safely but they can be a quick, easy, and cheap fish hide option for your green terror and oscar to help reduce the chances of aggression between the two.

Do I Need Sight Breaks In The Tank?

Another work around that you are able to take advantage of is to use sight breaks in the tank with your green terror and oscar in it to help reduce the visibility the two have of each other.

A sight break can be as simple as tank decorations, driftwood, rocks, long live plants as well as any number of other aquarium safe objects that are large enough to block the line of sight of one fish to the other as they swim around.

Can Green Terrors And Oscars Breed With Each Other?

Green terrors and oscars kept in the same aquarium tank as each other are not able to breed due to being from a different genus to each other. This allows you to keep both species in the same tank without having to worry about fry being produced.

The green terror is from the Andinoacara genus while the oscar is from the Astronotus genus meaning that the two are not able to cross breed with each other successfully.


Both the green terror and oscar are large, aggressive fish that need a lot of room in the tank. They should be added to the tank at the same time when they are young to reduce aggression between them and you will need to provide hiding places for both species. You can also use sight breaks in the tank to help reduce visibility between them.