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Oscar Fish Care

I would like to welcome another guest blogger, Lexi Jones. Lexi is one of our staff marine biologists, and a Supervisor in our retail store fish room.
Want to keep Oscars? This popular South American fish has been an aquarium favorite for decades, but keeping them often requires more than a beginner aquarist is prepared for despite their hardy nature. There are many things you must think about before buying these potentially large and high maintenance fish. 
Oscars can grow very large, very fast. It is not recommended to keep one Oscar in a tank smaller than 55 gallons, and some say not smaller than 75 gallons! The Oscar can reach an adult size of 14.” How fast they grow depends on water quality, how much you feed your Oscar, and tank size. Keeping them in a smaller tank may stunt their growth, cause deformities, and shorten their lifespan.

Oscars can also become very aggressive and territorial, thus they are best kept alone or with other Oscars in a VERY large tank. However, if you insist on keeping a different species with them, you can try keeping other cichlids of a similar size like Texas cichlids or Jack Dempsey cichlids.  Males, in particular, can fight each other for dominance in the aquarium, and it may lead to fatalities.
Oscars need very good filtration, they will put a heavy load on your biological filter. They are messy eaters and create a lot of fish waste. Please avoid undergravel filters; these can not handle the waste Oscars produce and create even more water quality issues. Large power filters or canisters are the best options. Partial water changes (at least 25% every 2-4 weeks) will also help keep the tank cleaner and keep the nitrates to a minimum. Testing the water quality once a week is recommended. The pH range for Oscars is be between 6.5 and 7.5; however, for success the pH must remain stable. Ammonia and nitrite readings should be zero, and nitrates should be as low as possible. The temperature that Oscars prefer is between 75 to 80 degrees Fahrenheit, so a heater is a must.
So, what can you feed your Oscar? They will eat pretty much anything that will fit in their mouth, but this is not healthy for them. To keep them healthy it best to feed them a variety of flake, pellet, and frozen foods. They come in various sizes for your baby Oscar or a full grown adult. Good choices include: Spectrum pellet foods, mysis shrimp, krill, beef heart, bloodworms, and night crawlers. We recommend not feeding live foods as a primary food source for your Oscars. Feeder goldfish can carry parasites and diseases, and are not a complete source of nutrition. Your oscars may appreciate a live treat on occasion, but ghost shimp or mollies may be better options.
Keep in mind that Oscars may look cute when they are little, but they can double or triple their size in a matter of months. Therefore, they absolutely need a large tank to be healthy and happy. Providing a large home from the beginning is much better than continuously moving them from tank to tank.
Thanks for the great blog Lexi, until next time.


  1. avatar

    I find it very disturbing that you only recommend a 20% water change on a monthly basis. Oscars make way too much waste to do only a monthly water change. Even if you had the best filtration on the tank I would recommend at least a weekly water change of 30 – 40%.

  2. avatar
    TFP Marine Biologist

    I agree that Oscars, and other large predators, can put an extreme demand on water quality. The article has been modified to recommend water changes of at least 25% monthly.
    While you may have had success with 30%-40% weekly water changes, I feel that changing that much water at once is far to dangerous. Removing that volume of water at once can cause rapid, and extreme, changes in water chemistry and temperature, as well as jeopardize the good nitrifying bacteria in your aquarium. Changing that volume of water should only be done in emergency situations. If you have proper mechanical filtration, and good water circulation in your aquarium, the filtration will trap the heavy waste produced, where it can be removed by regular filter maintenance.

    Thanks for your input


  3. avatar

    i just have a question can i put a small oscar with my big oscar

  4. avatar
    TFP Marine Biologist

    Though there is a possibility that you can mix oscars of slightly different size without incident, I don’t recommend it. There are many factors, some large oscars are docile and will “adopt” smaller tankmates, but aggression and predation may also occur depending on the size difference, sex, tank size, ect.

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