Comprehensive Guide to Oscar Cichlid Care, Breeding, and Tankmates

Basic “must know” information about Oscar fish:

• Scientific name: Astronotus ocellatus
• Maximum size (range): 30.0 - 40.0 cm (11.8 - 15.7 inches). They’re often sold as small juveniles, usually about 2.5 cm (approximately 1 inch) in size. However, Oscars can grow rapidly, increasing by 2.5 - 5 cm (1 - 2 inches) per month until they reach 20 cm (around 8 inches), after which their growth rate typically slows down by 50%.
• Recommended temperature: 24.0°C - 30.0°C (75.2°F - 86.0°F) - Oscars are not coldwater fish!
• Recommended water hardness (dGH): 4.0 - 18.0°N (71 - 321 ppm, 1.43 - 6.43 mEq)
• Recommended water pH: 6.5 - 7.5
• Origin: South America; For biotope inspiration, visit the South American Whitewater River guide if you wish to recreate a natural environment for these fish.
• Water quality: Ammonia and nitrites should be kept at zero; nitrates can reach up to 40 ppm (40 mg/l), but never introduce this species into an uncycled tank!
• Average lifespan: Typically ranges between 10-18 years, though some specimens have been known to live over 20 years.

Introduction to the Oscar Fish – Tank Setup

Oscar fish are famous for their intelligence and can become remarkably tame, often recognizing their owners over time. This trait has earned them the nickname “aquatic puppies.” Each Oscar fish has its own unique personality and behavior, much like other large cichlid species kept in aquariums. They can be quite particular about the tank’s layout and may frequently rearrange the décor to their liking, sometimes using their powerful jaws to move items around. It’s not uncommon for them to even attempt to spit décor out of the tank, regardless of its weight or size. Whether it’s plants, rocks, or driftwood, if an Oscar fish decides it wants something moved, it will find a way unless the décor is properly secured.

To accommodate their behavior, the tank décor should be kept simple. Use a sandy substrate as Oscar fish enjoy burrowing. Heavy rocks are an excellent choice for décor, but they should be placed in the tank before adding sand to prevent them from toppling over during burrowing. Hardy plants can also be included, such as Anubias, which have a taste that Oscars generally avoid.

Consider the thickness of the aquarium glass as well, since Oscars may occasionally bump into it. A glass thickness of at least 1 cm (0.4 inch) is recommended to reduce the risk of breakage. Ensuring proper safety measures is crucial when keeping Oscar fish.

Behavior and Tank Size per Specimen

One fascinating behavior of Oscars is their ability to "play dead," a tactic used in the wild to catch smaller fish. In an aquarium setting, Oscars may exhibit this behavior if they feel threatened by a more dominant tank mate - it's a form of submissive behavior. While Oscars are generally known for their aggression, this trait can be mitigated by providing an adequately sized tank. Astronotus ocellatus often coexist well with large Plecos and mid-sized South American cichlids (see the Tankmates section for more details). A fully grown Oscar requires about 150 liters (40 US gallons, 33 Imperial gallons) of water. However, a 150-liter tank is not sufficient for long-term housing; the tank should be spacious enough to allow for swimming and hiding. Display tanks are suitable for these fish.

Oscars can become more aggressive and territorial when kept in small groups of 2-3 individuals. This aggression can lead to injuries and open wounds, creating an environment conducive to fungal infections.

Pictures of the Oscar fish

Care and feeding habits of your Oscar

Effective care begins with selecting the right diet. Oscars are omnivores, and their ideal diet includes:

• Earthworms
• Bloodworms
• Tubifex
• Pellets
• Granules for cichlids
• Insects (for example flies)
• Crickets

Beef heart can be included in your Oscar's diet, but it should not be their primary food source. While some fish keepers consider feeder fish, such as guppies or goldfish, suitable, these can carry diseases that may affect your fish. Only use feeder fish if you are certain of their high quality, ideally by breeding your own. As mentioned earlier, Oscars need a lot of space, so it's important to emphasize this point. Comments on the article often reveal that aquarists tend to underestimate the necessary tank size.

Oscars prefer tanks with heavy rocks and driftwood and do not like bright lighting. Adding plants can enhance their habitat, though they might rearrange them to their liking. Due to their size and the volume of waste they produce, excellent filtration is essential - external canister filters are highly recommended. Regularly test the water for pH, ammonia, and carbonate hardness. Ammonia levels should be zero, and carbonate hardness should be 4 or higher. The ideal temperature range is between 26-28°C (78-82°F).

If you use submersible aquarium heaters, make sure to cover them with a suitable heater guard. Oscars can easily break the glass element of a heater, and a guard will also prevent any risk of burns to your Oscar from the heat.

Special thanks to Abel Guerrero for his picture.

Tank Mates

Optimal tank mates for Oscars include large Plecostomus and other sizable Neotropical Cichlids such as Texas Cichlids, Jack Dempseys, Salvini Cichlids, and other South American cichlids of similar or greater size. Among Oscars, Pink Tiger Oscars are typically the least aggressive, so avoid mixing them with Red or Tiger Oscars. The dominant fish in the tank is usually the one that eats first and most during feeding. Be cautious when adding Oscars to a community tank as they may end up eating smaller species. However, fast-moving tetras may coexist with Oscars if introduced together as juveniles.

Breeding Oscar Fish

Breeding Oscars is relatively straightforward if you maintain a pair. Emphasize the importance of high water quality and stable conditions for successful breeding. Clean water with a stable temperature around 28°C (82°F) is crucial. Breeding is challenging in colder water or water with high ammonia levels, odors, or poor quality. The following methods are effective:

• Add oak bark extract to the tank daily
• Lower the temperature for about 2 weeks before the expected breeding period
• Increase the temperature to 28°C (82°F) after 2 weeks
• Use subdued lighting
• Include flat rocks in the tank

If the Oscars are in the same tank before breeding, they might need some encouragement. If the previously mentioned methods do not work, try removing the male for one to two weeks. Feeding Oscars live or frozen food can also help trigger breeding. Use heavy rocks in the tank as the fish will clean them to lay eggs. Large driftwood can also facilitate the breeding process. Overall, their breeding behavior is similar to other large South American cichlids.

After the eggs are laid, both parents will guard them. It’s not necessary to remove the eggs, but be aware that stressed pairs might eat them. Young Oscars often consume their first batch of eggs, though this usually improves with experience. Oscars typically reach sexual maturity between 18 to 24 months. Once the fry absorb their egg sac, they should be fed Artemia salina, Daphnia, egg yolk, or microworms.

This article is also available in German: Der Fisch Oscar.

Picture

Special thanks to Tamri Shavi for the image!

Additional Questions and Answers

Following the integration of aqua-fish.net/answers with our articles, we've compiled common questions that fishkeepers frequently ask. Some of these questions may be partially addressed in the article, but listing them here provides a clearer overview. Feel free to submit your own questions using the form at the bottom of this page, making sure they are unique and not already covered.

• What is the smallest tank size suitable for an Oscar fish?

  Answer: The minimum tank size recommended for an Oscar fish is 300 liters (approximately 80 US gallons or 66 Imperial gallons). Oscars can grow to lengths of 30-40 cm (11.81 - 15.75 inches) quite easily, so providing ample space is crucial for their well-being.

• What distinguishes an Oscar fish from a Jack Dempsey?

  Answer: The Oscar fish (Astronotus ocellatus) is generally more peaceful, whereas the Jack Dempsey (Cichlasoma octofasciatum) is known for its aggressive behavior. Additionally, Oscars are native to South America, while Jack Dempseys come from Central America.

• Which fish are suitable tankmates for an Oscar fish?

  Answer: Oscars are best kept with peaceful fish of similar size. It is advisable to choose species from South America to match their water and habitat requirements. Avoid adding smaller fish, as Oscars may view them as prey. Suitable companions include other large cichlids like the Pacu and adult plecostomus.

• Why do my Oscar fish fight?

  Answer: Oscars are territorial, like many cichlid species. They may fight to establish dominance and claim their own space if they were not introduced to the tank together.

• What toys can I give to my Oscar?

  Answer: Oscars are quite intelligent and can benefit from toys to stay engaged. Consider using pieces of bogwood or unsecured plastic plants as toys. These can provide enrichment and help prevent boredom.

• What size is the biggest Oscar fish?

  Answer: Oscars can reach lengths of up to 16 inches (40.64 cm) and can weigh as much as 3.5 pounds (1.58 kg). Ensure you provide a sufficiently large tank to accommodate their full growth.

• When are Oscars mature enough to lay eggs?

  Answer: While some keepers suggest that Oscars reach maturity at around 12 months, it is generally accepted that they become sexually mature between 16 and 18 months of age.