Care guide · Freshwater · fish
Oscar care guide
Astronotus ocellatus
The Oscar (Astronotus ocellatus) is an intelligent, striking South American cichlid that may look small when sold as a juvenile but needs substantial adult space and strong filtration. Plan on a tank at least about 150 cm long and 450 litres for one adult; a pair needs considerably more. Oscars accept varied foods and may swallow small fish. They are not a routine community fish, so plan housing for the long term before buying one. Consider its adult size, long lifespan and the amount of waste produced by a large fish. A juvenile Oscar is not evidence that a small aquarium will remain suitable; buy only when the full-size setup is ready and biologically stable.
Plan your aquarium →At a glance
- Temperature
- 21–27 °C
- pH
- 6.0–7.5
- GH
- 5–20 °dGH
- Aquarium length
- At least 150 cm
- Minimum aquarium volume
- At least 450 L
- Adult size
- Up to 35 cm
- Group size
- At least 1 individuals
- Lifespan
- 10–20 years
- Temperament
- Territorial, Predator
About this species
The Oscar is a member of the family Cichlidae. Seriously Fish reports a maximum of about 35 cm standard length and a typical lifespan of 10–20 years. It has a robust body, a large mouth and often an eye-like spot near the tail. Tiger, red, albino and long-finned forms are sold in the trade. A colour form does not by itself establish a fish’s wild origin or lineage.Natural habitat
Astronotus ocellatus occurs widely across the Amazon region and neighbouring South American waters. It is often found in slow or still forest waters among submerged roots and marginal vegetation. In an aquarium, provide open swimming room with sturdy cover. Secure rocks and wood because Oscars move substrate and decorations.Aquarium and layout
The sources describe a large setup for one adult: Seriously Fish lists a 150 × 60 cm tank base, while Fishkeeping gives 450 litres and a 48 × 24 × 24 inch tank. Use at least about 150 cm length and 450 litres as a cautious baseline, with more room as the fish grows. Fishkeeping recommends a much larger 690-litre, 183-cm-long aquarium for a pair. Use strong filtration, a mature filter and secure heating. Choose an easy-clean substrate and monitor ammonia, nitrite and nitrate regularly.Water conditions
Fishkeeping lists 21–27 °C and pH 6.0–7.8; Seriously Fish gives 20–28 °C, pH 6.0–7.5 and hardness of 5–20 dGH. The guide presents the overlapping temperature and pH ranges, not a proven single optimum. Keep conditions stable and adjust maintenance to measured water quality. Avoid rapid attempts to alter pH or hardness.Behaviour and group size
Oscars are large and may become territorial. Any fish that fits in the mouth can be prey. Fishkeeping advises against ordinary community stocking, while Seriously Fish stresses careful tankmate selection. A single Oscar is usually the simpler option. Combine only with robust, suitably sized fish in a very large aquarium, and monitor behaviour and feeding. No particular tankmate is listed as a verified match on this guide.Feeding
Use a complete cichlid pellet or stick as the staple and vary it with suitable frozen foods. The species naturally eats a range of animal prey, but small aquarium fish may be swallowed. Do not use feeder fish or mammal meat. Measure portions, avoid overfeeding and remove leftovers to limit waste.Breeding
Oscars form pair bonds and lay eggs on a cleaned, flat surface. Give a pair its own large aquarium with flat stones or similar spawning sites. Seriously Fish describes a pair forming from a group of juveniles; remove the other fish once a pair forms. This is not a reason to keep six adult Oscars together. Breed only with sufficient space and a plan for the many offspring.Sources & review
This care guide draws on several specialist sources and was last checked on .