Identity and search names

Common name
Oscar
Scientific name
Astronotus ocellatus
Other names
Oscar, Tiger oscar, Velvet cichlid, Astronotus ocellatus
Category
Freshwater fish
Group
Large cichlids
Origin
Tropical South American floodplains and slow rivers, including major Amazon and connected northern drainage systems
Review outcome
PASSED

Environment and housing

Environment
Freshwater
Care level
Advanced
Adult size
Commonly 30–40 cm, with published records around 45 cm total length
Expected lifespan
About 10–20 years
Minimum housing
At least 600 L for one adult; a compatible pair requires a substantially larger aquarium
Temperature
23–28 °C
pH
6.0–8.0
Hardness or minerals
Soft to moderately hard
Salinity
Freshwater
Lighting
Moderate with shaded refuge
Social structure
Keep one adult or a genuinely compatible pair; do not force two mature fish together
Placement or swimming zone
All levels, especially middle and lower water
Temperament
Large territorial cichlid with individual temperament and intense breeding defence
Compatibility
Only use large robust tankmates in substantially larger systems; be prepared to separate incompatible adults
Habitat structure
Very large aquarium with powerful filtration, open turning space, secured smooth décor, protected heaters and a tight lid

Feeding and nutrition

Diet
Aquatic invertebrates, fish, crustaceans, fruits and balanced large-cichlid prepared foods
Feeding frequency
Feed measured varied meals once daily or several times weekly for adults according to body condition; avoid feeder fish and overfeeding

Breeding and reproduction

Breeding or reproduction
A compatible pair cleans a flat surface, lays eggs and guards the site and fry. Pair bonds can fail violently, so separation equipment is mandatory
Parental care
Strong biparental egg and fry care

System demands

Filtration
Use mature biological filtration sized for the full adult group and feeding load, with intake protection where juveniles, long fins or small fish are present. Provide steady turnover without preventing normal swimming or resting.
Aeration
Maintain strong surface gas exchange and stable dissolved oxygen. Increase aeration during warm weather, medication, transport recovery, breeding crowding or any ammonia or nitrite event.
Maintenance
Test ammonia, nitrite and nitrate, remove waste from feeding and shelter zones, and perform regular temperature- and chemistry-matched water changes before nitrate or dissolved organics accumulate.

Detailed husbandry

Identity scope
This profile applies to Astronotus ocellatus, while recognising that wild Astronotus diversity and some aquarium lineage labels remain taxonomically complicated. Domestic colour strains are not wild localities.
Adult size and space
Commonly 30–40 cm, with published records around 45 cm total length. At least 600 L for one adult; a compatible pair requires a substantially larger aquarium. Plan around adult dimensions, activity, social structure, aggression and waste production rather than sale size.
Social structure
Keep one adult or a genuinely compatible pair; do not force two mature fish together
Placement or swimming zone
Primary zone: All levels, especially middle and lower water. Keep that zone usable for movement, feeding and refuge.
Feeding ecology
Aquatic invertebrates, fish, crustaceans, fruits and balanced large-cichlid prepared foods
Feeding plan
Feed measured varied meals once daily or several times weekly for adults according to body condition; avoid feeder fish and overfeeding
Water stability
Maintain 23–28 °C; pH 6.0–8.0; hardness/minerals: Soft to moderately hard. Stable oxygenation and nitrogen-cycle control matter more than chasing one exact number.
Adult projected load
Plan capacity for Keep one adult or a genuinely compatible pair; do not force two mature fish together at the documented adult size (Commonly 30–40 cm, with published records around 45 cm total length) in At least 600 L for one adult; a compatible pair requires a substantially larger aquarium. Include feeding intensity, territorial behaviour and breeding growth rather than counting sale-size juveniles.
Filtration
Use mature biological filtration sized for the full adult group and feeding load, with intake protection where juveniles, long fins or small fish are present. Provide steady turnover without preventing normal swimming or resting.
Aeration
Maintain strong surface gas exchange and stable dissolved oxygen. Increase aeration during warm weather, medication, transport recovery, breeding crowding or any ammonia or nitrite event.
Maintenance
Test ammonia, nitrite and nitrate, remove waste from feeding and shelter zones, and perform regular temperature- and chemistry-matched water changes before nitrate or dissolved organics accumulate.
Habitat structure
Very large aquarium with powerful filtration, open turning space, secured smooth décor, protected heaters and a tight lid
Compatibility plan
Only use large robust tankmates in substantially larger systems; be prepared to separate incompatible adults
Breeding plan
A compatible pair cleans a flat surface, lays eggs and guards the site and fry. Pair bonds can fail violently, so separation equipment is mandatory Parental care: Strong biparental egg and fry care.
Quarantine
Quarantine new fish in a separate cycled aquarium with dedicated equipment. Match temperature and mineral chemistry gradually, confirm feeding and normal respiration, and never add transport water to the established aquarium.
Welfare checks
Maintain the stated adult space and social structure, verify feeding and intervene early when injury, exclusion, weight loss, abnormal respiration or altered behaviour appears. Oscars are large, messy, powerful and frequently released when they outgrow tanks. A 450 L aquarium is not adequate adult housing for this profile.
Biosecurity and release
Never release fish, fry, eggs, aquarium water, sediment, plants or live foods into drains, dams or natural waterways. Confirm current Australian import conditions and South Australian possession, trade and movement rules before acquisition or transfer.
Main risk
Oscars are large, messy, powerful and frequently released when they outgrow tanks. A 450 L aquarium is not adequate adult housing for this profile.
Overridable warnings
Oscars are large, messy, powerful and frequently released when they outgrow tanks. A 450 L aquarium is not adequate adult housing for this profile. Any override must still preserve adult space, social welfare, stable chemistry, oxygen and filter capacity.

Welfare and risk

Welfare checks
Maintain the stated adult space and social structure, verify feeding and intervene early when injury, exclusion, weight loss, abnormal respiration or altered behaviour appears. Oscars are large, messy, powerful and frequently released when they outgrow tanks. A 450 L aquarium is not adequate adult housing for this profile.
Main warning
Oscars are large, messy, powerful and frequently released when they outgrow tanks. A 450 L aquarium is not adequate adult housing for this profile.
Biosecurity
Never release fish, fry, eggs, aquarium water, sediment, plants or live foods into drains, dams or natural waterways. Confirm current Australian import conditions and South Australian possession, trade and movement rules before acquisition or transfer.

Sources

Source note

Current identity or scope, husbandry, system-demand, welfare and Australian biosecurity evidence checked; active retired-source links removed; all AquaNexus wording is original.

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