How Many Oscars Can I Keep In A 55 Gallon Tank? (Answered!)

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You should keep a maximum of 1 oscar in a 55-gallon tank. Oscars are big fish. They can reach 12” and sometimes larger. They eat a lot of food and create a lot of waste. The more space they have, the more stable their environment and the better they will do.

I have been keeping, and breeding, Oscars for over 30 years. During that time I have kept almost every color strain you see for sale. Today, one of the most enjoyable aquariums in my fish room is my trio of Lemon Oscars. That tank never fails to impress anyone who comes into my fish room!

I often get asked the question ‘How many Oscars can I keep in a 55-gallon tank?’ The answer I always give is one Oscar! Unfortunately, that isn’t the answer people are looking for.

A 55-gallon is a large tank to a lot of people, and keeping just one fish in a 55 gallon feels like a waste of space. I like to keep a single Oscar in a minimum of 75 gallons wherever possible.

How Much Space Does An Oscar Need?

For a single oscar, I always aim for a minimum of 75 gallons, followed by a further 25-50 gallons per additional fish. As Oscars grow to around the 12” mark, they not only need ample space to physically swim in, but they also produce A LOT of waste. Oscars eat lots and poop lots. Not only that, but they are incredibly messy eaters.

Oscars don’t just have teeth in their jaws, they also have them in their throats. If you’ve ever watched an oscar eating fish pellets, you’ll have seen the cloud of ‘dust’ that comes out of their gills whilst they’re eating.

This uneaten food then builds up in the tank and breaks down, raising the ammonia levels.

Oscars are also incredibly strong. They will happily rearrange the rocks and decorations you have lovingly placed around their aquarium. To reduce their ability to move rocks, you should use larger, heavier rocks. Large rocks in a small tank won’t allow the Oscars enough swimming space.

What Size Tank For Two Oscars?

A forever tank for 2 Oscars would need to be 100 gallons or more. Anything smaller won’t give the adult Oscars enough space to swim around in and you will become a slave to water changes. A 100-gallon tank will probably measure in the region of 72½” x 18½” x 19 3/8″ (L x W x H).

This is a good-sized tank for your Oscars. Even once you add in the substrate and large rocks, there will still be plenty of space for your two Oscars.

What Size Tank For Juvenile Oscars?

Clearly, a 3” juvenile oscar will be fine in a smaller tank, but I still recommend starting off with a tank large enough for the adult fish. Oscars grow like weeds! They can easily put on 8 to 10 inches in their first year. This often catches people off guard.

So often people set up a 40 gallon for their two-inch Oscars, and have every intention of replacing the tank before the Oscars reach maturity. The problem is real-life throws spanners in the works. one month the car needs fixing, the next the heating has packed up.

Before you know it, the Oscars are 12” long and the tank still hasn’t been replaced. Start off with the Oscars forever tank, and you know you’re sorted, no matter how quickly they grow.

What Do You Do If You Have Too Many Oscars In A Tank?

If you find yourself with more Oscars in a tank than you should (whatever the size of the tank), there are a few things you can do to improve the Oscar’s situation.

  • Re-home one or more oscars – This may seem like a drastic step, but if you can reduce the number of fish in the tank, those that are left will have more space. It can be tricky finding someone who is prepared to offer space for a large oscar. Unfortunately, there are many oscars in need of a new home. Ask around your local fish club and in your local fish store. Someone may know of a member or customer that has large tanks and is happy rehoming fish. The Ohio Fish Rescue are a great example of an organisation helping rehoming large fish.

  • Add more filtration – Because oscars are so messy, the waste builds up quickly in the tank. Adding a second or even third filter can increase circulation and speed up the removal of particles in the water. Servicing those filters removes that waste from the system altogether.

  • Change more water – No matter how many filters you add; you will still need to change water in your aquarium. Filters are great at converting the fish waste into relatively harmless nitrate, but that nitrate can build up to harmful levels. The best way to get the nitrates out is to drain off around 50% of the tank water each week and top it up with fresh water.

In Conclusion

A 55-gallon tank is a decent size tank. For many people 55 gallons represents a ‘big’ tank, it is just not big enough for more than one oscar. Consider a 125 or 155 gallon for 2to 3 Oscars.

If you are yet to make your tank purchase, and one fish isn’t enough for you, consider keeping a different fish or take the time to save up for a bigger tank. Please don’t make the classic mistake of ‘I’ll buy the 55 today, then get a bigger tank in a few months. Oscars grow really fast, about 1” a month. Before you know it the 55 gallons will be too small and you may not be in a position to buy that 120 gallons you had your eye on.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James

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