How to Take Care of an Oscar Fish

Oscars grow quite large, so their housing can be challenging.
Oscars grow quite large, so their housing can be challenging. (Image: BLUEXHAND/iStock/Getty Images)

Hailing from the Rio Ucayali and Upper Amazon river drainages, oscars are popular aquarium fish, despite being a large and aggressive species. Part of the fish's popularity comes from their outgoing personalities. Some learn to accept food from their keepers’ fingers. Growing to 13 inches in length and nearly 2.5 pounds in weight, oscars require spacious accommodations. Because they are aggressive, oscars are best kept singly; males may kill even their breeding partners.

Things You'll Need

  • Aquarium, 70 gallons or larger
  • Aquarium stand or stable platform
  • 1 pound of aquarium sand per gallon of aquarium space
  • Decorations (optional)
  • Garden hose
  • Spring-loaded clips (optional)
  • Water conditioner
  • Water heater
  • Thermometer
  • Canister-style water filter
  • Nitrifying bacteria
  • Light fixtures
  • Timer (optional)
  • Water test kit
  • Fish food
  • Siphon attachment (optional)
  • Bucket

Setting Up the Aquarium

Place the aquarium on a stand or other stable resting place.

Add the sand and decorations to the bottom of the tank. The sand should be at least 1 inch deep.

Fill the tank with clean tap water and add the water conditioner. Water conditioners neutralize chlorine, chloramine and other harmful compounds in the tap water.

Place the heater in the aquarium and set the thermostat between 72 and 84 degrees Fahrenheit. Use the digital thermometer to measure the water temperature. Allow the temperature to stabilize -- which may take 24 hours or more -- before proceeding.

Set up the canister filter by filling the reservoir with water and placing the intake hose in the aquarium. Place the output hose at the opposite end of the tank to increase the amount of water movement in the tank. Turn the filter on. It should begin drawing water into and pumping water out of the canister. Some canister filters must be primed before use; follow instructions for pouring water into a small opening on the unit.

Add the nitrifying bacteria to the water. Adding nitrifying bacteria to the aquarium allows you to avoid the long and tricky process of building this bacteria up with live fish.

Place the light fixture on top of the aquarium. If you wish, you can plug the light fixture into a timer switch so you do not have to turn the lights on and off every day. Set the timer for a 12-hour light cycle.

Test the water quality with the water test kit to ensure that the water is suitable before adding the oscar. Be sure that the water does not have any detectable chlorine or chloramine. Additionally, the water should be neutral to acidic, and the pH should be between 6.6 to 7.0. Writing for Tropical Fish Hobbyist Magazine, freelance pets writer Sara Jackson says the nitrates must not exceed 10 parts per million, for the long-term health of your fish.

Once you are satisfied that the water's chemistry and temperature are within the acceptable range, you can add the oscar. "Float" the oscar for about an hour before placing your pet directly in the aquarium water. To float your oscar, place him in a clear plastic bag that is full of water from the aquarium he has been swimming in. Then float that bag on top of the aquarium water. This allows the water in the bag to slowly reach the same temperature as the water in the new aquarium, preventing the oscar from being shocked by a sudden change in water temperature. As the oscar is floating, add a few ounces of the aquarium water to the bag every 10 minutes. This will allow the oscar to acclimate to the new water chemistry.

Caring for an Oscar

Feed your oscar one time each day, six days per week. Many aquarists overfeed their fish, which ruins the quality of the water. Feed your oscar only the amount of food he can eat in about 30 seconds. Overfeeding your oscar is detrimental to the tank's water clarity and chemistry. The additional organic material will decay slowly and produce ammonia, which is harmful to your fish. Be sure to offer a wide variety of foods, including cichlid pellets, bloodworms, earthworms, flake food and small fish.

Test the aquarium water with the test kit at least once per week. Ensure that all facets of water quality are appropriate.

Once per week, conduct a 25 percent to 50 percent water change by using the siphon or garden hose and a bucket to empty some of the old aquarium water. If you choose to replace 50 percent of the water weekly, do so slowly, over a period of 12 to 24 hours. Use the siphon or garden hose to fill the large bucket with water. Treat the replacement water with conditioner and nitrifying bacteria, and be sure that the water is between 72 and 84 degrees Fahrenheit before adding it to the tank. It may take several such cycles of filling the bucket, treating the water and then adding it to the tank before you are finished.

Tips & Warnings

  • Avoid using plants that must be anchored in the substrate. While oscars appreciate plants and places to hide, they are likely to uproot any that are buried in the substrate. Artificial plants or live, floating plants are better options. Alternatively, you can use plants that are planted in small containers.
  • Spring-loaded clips are helpful for keeping the siphoning hose in place while you travel to and from the faucet.
  • Always be careful when using electrical appliances near water.
  • If you must add another fish to your oscar's aquarium, select one at least as large as the oscar.

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