Species profile
Oscar
Astronotus ocellatus
Semi aggressive
Moderate care
450 L minimum aquarium
25–35 cm adult size
All levels
Can be kept singly
About this species
General notes for hobby use.
The Oscar is a large, intelligent and long-lived South American cichlid. Aquarium adults commonly reach about 25–35 cm, although wild specimens have been recorded at 45.7 cm total length. Plan a single adult around a tank footprint of at least 180 × 60 cm and roughly 450 litres or more; additional Oscars or tankmates require substantially more room. Provide powerful, easily maintained filtration, good oxygenation, regular substantial water changes and sturdy decor without sharp edges. Oscars produce heavy waste, often uproot plants and commonly rearrange their surroundings.
Water parameters
Suggested general range for long-term care.
Temperature
23–27 °C
pH
6–8
GH
5–19 dGH
KH
Not yet documented
Flow preference
Low–moderate
Data confidence
Verified
Behaviour
General behaviour traits used by TanksConnected compatibility checks.
Minimum group size
Can be kept singly
Tank zone
All levels
Territory level
Moderate
Predation risk
Small fish
Bioload factor
3
A robust cichlid with intelligent but highly individual behaviour. Oscars are not always relentlessly aggressive, but territoriality can increase sharply during pair formation and spawning. Keep one alone unless a compatible pair or group has been deliberately established in a much larger aquarium. Fish and invertebrates small enough to fit in the mouth may be eaten. Avoid tiny, timid or extremely aggressive tankmates, and always have a realistic plan for separating incompatible individuals.
Compatibility flags
Quick cautions for common tank-planning issues.
Fin nipper
No
Plant safe
Caution
Shrimp safe
No / caution
Snail safe
No / caution
Cave breeder
No
Digs substrate
Yes
Jump risk
Yes
Natural history & care
Research-backed context for long-term aquarium care.
Lifespan
10–20 years
Diet type
Omnivore
Minimum aquarium volume
450 L
Minimum footprint
180 × 60 cm
Accepted scientific name
Astronotus ocellatus
Alternative names
Velvet Cichlid, Marble Cichlid, Tiger Oscar, Apaiari
Native range
Native principally to the Amazon River basin in South America, including records from Brazil, Peru, Colombia and French Guiana. Older references often include the Orinoco basin, but a 2022 integrative taxonomic study described Orinoco and Gulf of Paria populations as Astronotus mikoljii. Locality-based identification should therefore be treated cautiously. The Oscar has also been introduced outside its native range.
Natural habitat
Occurs in quiet, shallow and slow-moving freshwater habitats such as backwaters, canals, ponds and flooded margins, commonly over mud or sand. Roots, branches and other submerged cover provide shelter and ambush positions. In an aquarium, retain generous open swimming and turning space, use sturdy rounded decor, and avoid a constant powerful current directed at the fish.
Diet & feeding
An opportunistic omnivore with a strong preference for animal foods. Wild foods include insects and larvae, worms, crustaceans, small fish and seasonal fruits, nuts and other plant material. Use a quality complete large-cichlid pellet as the staple, supplemented with suitable foods such as earthworms, insects, krill and varied frozen foods. Avoid routine feeder fish because they can transmit disease and provide inconsistent nutrition. Do not feed mammalian or poultry meat. Control portions because Oscars beg readily, and overfeeding quickly damages body condition and water quality.
Breeding & sexing
Research-backed guidance for identifying sexes and reproductive behaviour.
Sexing
Males and females are externally very similar, so colour, fin shape and general body shape are unreliable. Mature fish are most reliably sexed by observing the breeding tubes or by careful vent examination: the female has a larger, blunter ovipositor while the male papilla is smaller and more pointed. Pair formation and confirmed spawning provide stronger evidence than appearance.
Breeding
Open-substrate, biparental spawner. A compatible pair cleans a flat rock, piece of wood or excavated site and may deposit hundreds to thousands of eggs. Both parents guard the eggs and fry. Eggs typically hatch after around three to four days, after which the parents may move the larvae to a shallow pit. Spawning aggression can be severe. Breeding should only be attempted with adequate space and a realistic plan for large numbers of juveniles.