Oscar fish - Astronotus ocellatus

Scientific name: Astronotus ocellatus

Common name: Oscar fish

Family: Cichlidae

Usual size in fish tanks: 30 - 40 cm (11.81 - 15.75 inch)

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Recommended pH range for the species: 6.5 - 6.5

Recommended water hardness (dGH): 4 - 18°N (71.43 - 321.43ppm)

0°C 32°F30°C 86°F

Recommended temperature: 24 - 30 °C (75.2 - 86°F)

The way how these fish reproduce: Spawning

Where the species comes from: South America

Temperament to its own species: peaceful

Temperament toward other fish species: peaceful

Usual place in the tank: Middle levels

Food and Feeding

Oscar fish (Astronotus ocellatus) are omnivorous and have a voracious appetite, eating anything that fits in their mouth. Their diet should be diverse, focusing on insects, crustaceans, worms, and plant matter. High-quality cichlid pellets or sticks form an excellent staple diet, supplemented with various foods like krill, prawns, brine shrimp, bloodworms, and even vegetables such as peas, spinach, cucumber, zucchini, and fruits like melon and bananas. Young Oscars enjoy smaller foods like brine shrimp, but as they grow, they need larger food items. Avoid feeding them poultry, mammal parts like beef heart, or feeder fish such as goldfish. These foods contain high levels of fat and thiaminase, which can be harmful to Oscars. The best feeding schedule is to offer small amounts of food several times a day and have one fasting day per week to aid digestion and prevent overeating.

Origin

Oscars are native to the slow-moving rivers and streams of the Amazon River basin in South America. They are commonly found in countries such as Brazil, Colombia, Peru, and Venezuela. Their preferred habitat includes slow or still waters with heavy vegetation and plenty of submerged plants. In the wild, these fish are often found in areas with a muddy or sandy substrate where they can hunt for small fish, invertebrates, and plant matter.

Sexing

Sexing Oscars is notoriously difficult. Many methods have been suggested, such as examining the shape and size of the fins or the presence of certain physical traits, but these are often unreliable. The only surefire way to determine the sex of an Oscar is to observe them during breeding. The female will be the one releasing eggs, while the male fertilizes them. Sometimes two females may display breeding behavior, but if the eggs remain unfertilized and turn white, it's likely that both fish are female.

Breeding

Breeding Oscars can be a challenge primarily because of the difficulty in determining the sex of the fish and the need for a compatible pair. To encourage breeding, provide a spacious tank with a flat rock substrate, subdued lighting, and no tank mates. Slowly raise the water temperature and perform large water changes to simulate the warm spring rains of their natural habitat, which often triggers spawning behavior. During breeding, the pair will swim around each other, clean the breeding site, and lay up to 2,000 eggs. Fertilized eggs turn yellow-orange within 24 hours, while non-fertilized eggs remain white. Inexperienced parents may eat their eggs or fry, but with practice, they will improve in caring for their young. If the parents eat the eggs or fry, consider removing them to a separate tank and simulate the fanning motion that the parents usually perform. The eggs hatch within 3 days, and the fry become free-swimming after an additional 4 days. Feed the fry newly hatched brine shrimp and keep the water exceptionally clean using a sponge filter and daily water changes.

Lifespan

Oscars are a long-term commitment for aquarists, with a potential lifespan of up to 18 years when provided with proper care. Their longevity depends on maintaining high water quality, as they are messy eaters that produce significant waste. Poor water conditions can lead to health issues, so regular maintenance, including frequent water changes and efficient filtration, is crucial to ensure a healthy and long life for these fish.

Tank Requirements

Oscars are large fish requiring ample space. A single Oscar requires a minimum tank size of 300 liters (75 gallons), with an additional 200 liters (50 gallons) for each additional Oscar. Given their size and strong personalities, they are known to rearrange the tank setup, so choose decorations wisely. Use smooth rocks, large driftwood, and sturdy plants attached to decor, as they may uproot or destroy fragile plants. Opt for a sandy substrate or fine gravel that is gentle on their bellies while allowing them to dig without harming themselves. Avoid sharp-edged decorations to prevent injury.

Oscars are notorious for messing with equipment like internal filters and heaters, so an external canister filter with a built-in heater is recommended. Choose a filter that can process the tank's water volume at least eight times per hour to handle the waste produced. Ensure the tank has a secure lid, as Oscars are known to jump. They do not need bright lighting; in fact, some prefer dim or no light, so provide subdued lighting to avoid stress. You can even place floating toys like ping-pong balls to keep them mentally stimulated.

Tank Mates

While Oscars can be peaceful toward similar-sized tank mates, they will see smaller fish as potential food. Ideal tank mates include other large, non-aggressive fish like Silver Dollars, Severums, and Plecos. However, even with similar-sized companions, it's important to monitor behavior, as aggression can still occur, especially as Oscars mature. Avoid overly aggressive fish that may bully the Oscar. If housing multiple Oscars, ensure there is plenty of space to reduce territorial disputes. It's generally advised to avoid keeping three Oscars in one tank, as two may gang up on the third.

Short Description

The Oscar fish (Astronotus ocellatus) is a large and highly intelligent cichlid known for its striking appearance and strong personality. They come in various color variants, including Tiger Oscar, Red Oscar, Albino Oscar, and more. Oscars are known for their interactive behavior, often recognizing their owners and even allowing gentle petting. However, they require a spacious and well-maintained aquarium to thrive. Although they are peaceful toward similarly sized fish, they can be aggressive toward smaller tank mates. With a lifespan of up to 18 years, Oscars are a long-term commitment, offering aquarists a fascinating and dynamic aquarium inhabitant. For further reading, visit this article on raising and breeding Oscar fish.

Pictures

Special thanks to Abel Guerrero for his picture. Other pictures were bought from jjphoto.dk. Also thanks to Ramar! Some pictures were provided by Damian, Amy and other contributors.