A highly intelligent, large, and personable South American cichlid often described as a 'water dog'. They are notoriously messy eaters, heavy waste producers, and will enthusiastically rearrange tank decor and uproot plants. Any fish small enough to fit in their mouth will be eaten. They require excellent filtration and strict water maintenance.
Oscar At a Glance
Oscar Tank Requirements
Will Oscar fit in your tank?
Care guides tell you what Oscar needs, the next question is whether your tank can safely provide it. Test Oscar against your tank size, maintenance needs, and the fish you already keep before you buy.
Useful setup supplies
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Oscar Water Parameters
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Oscar Temperament & Compatibility
Oscar Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Standard Adult
The full-grown adult Oscar. Due to their extreme bioload and size, they require a 75+ gallon tank for a single specimen and heavy filtration.
Differs in 1 trait from base species
Also known as: Tiger, Red, Albino, Adult Oscar
Juvenile (Grow-out)
Young Oscars commonly sold at 5-10cm. They grow incredibly fast (up to an inch a month) and will quickly outgrow a starter tank. Must be upgraded to a 280L+ tank within a few months to prevent stunting.
Differs in 5 traits from base species
Also known as: Baby Oscar, Small Oscar, Juvenile
Veiltail / Long Finned
A selectively bred morph with long, flowing fins. They require lower flow to prevent fin damage and exhaustion, and should not be kept with fin-nipping tank mates.
Differs in 2 traits from base species
Also known as: Longfin Oscar, Veiltail Oscar
Oscar Care Guide Summary
The Oscar, scientifically known as Astronotus ocellatus, belongs to the Cichlids - South American family group. Adults reach a maximum size of approximately 30 cm and have a compressed body shape with a fast growth rate. Classified as aggressive, this species primarily occupies the mid-level and bottom zones of the aquarium and produces a extreme level of biological waste.
To thrive, the Oscar requires a freshwater only aquarium with a minimum volume of 280 litres and a tank length of at least 120 cm. Water temperature should be maintained between 23°C and 27°C, with a pH range of 6–7.5 and a general hardness of 5–15 dGH. A moderate water flow is preferred.
Due to its specialist needs, the Oscar is best suited for fishkeepers who can provide a carefully planned setup. This species is available in 3 varieties: Standard Adult, Juvenile (Grow-out), and Veiltail / Long Finned. Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Oscar Habitat Setup
When setting up an aquarium for the Oscar, a moderate water flow best suits their natural preferences. Because this species occupies the mid-level and bottom zones, the aquarium layout should prioritise open swimming space in the centre of the tank for free movement and sufficient floor space with hiding spots among rocks, wood, or dense planting. Useful additions include a sand substrate to accommodate their sifting behaviour, smooth gravel or rounded substrate to protect their sensitive barbels, and driftwood, which can serve as both a hiding place and a dietary supplement. Keepers should note that expect substrate disturbance, so lightweight décor should be secured and live planted layouts may be difficult to maintain, as this species tends to uproot or consume vegetation.
Oscar Compatibility Notes
Classified as aggressive, the Oscar is adaptable and can be kept singly or in a small group, offering flexibility when planning a community tank. When choosing tankmates, any fish small enough to fit in its mouth will likely be eaten, territorial behaviour may cause issues if hiding spots or floor space are limited, and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the mid-level and bottom zones can help reduce competition and territorial overlap.
Oscar Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Oscar.
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
180 Gallon Standard
350 Liter (120cm Deep)
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Frequently Asked Questions About Oscar
How big does Oscar get?
Oscar (Astronotus ocellatus) typically reaches a maximum adult size of approximately 30 cm. They have a compressed body shape and a fast growth rate.
What tank size does Oscar need?
A minimum aquarium volume of 280 litres and a tank length of at least 120 cm are recommended for Oscar. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Oscar need?
Oscar thrives in freshwater only conditions with a temperature range of 23–27°C, a pH between 6 and 7.5, and a general hardness of 5–15 dGH. A moderate water flow is preferred.
Is Oscar peaceful or aggressive?
Oscar is classified as aggressive with an aggression score of 7 out of 10. Careful tankmate selection is essential to avoid conflict.
Can Oscar live alone?
Yes, Oscar can be kept singly or in a group. They are flexible and adapt well to both setups.
Does Oscar have any special tank requirements?
Yes. Oscar benefits from sand (sifters), smooth gravel (sensitive barbels), and driftwood (digestion/hiding) in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Plants That Suit Oscar
These plants pair well with Oscar based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Afzel's Anubias
Anubias afzelii
Anubias Barteri
Anubias barteri
Belinda's Buce
Bucephalandra belindae
Buce Motleyana
Bucephalandra motleyana
Congo Anubias
Anubias heterophylla
Dwarf Buce
Bucephalandra pygmaea
Fish Similar to Oscar
Freshwater Angelfish
Pterophyllum scalare
The most iconic South American Cichlid, known for its distinct arrowhead shape and majestic fins. While domestic strains are hardy, they remain cichlids: they are semi-aggressive predators that will eat any fish small enough to fit in their mouths (like Neon Tetras). They form loose shoals as juveniles but pair off and become territorial as they mature. Height is more important than length for this species.
Midas Cichlid
Amphilophus citrinellus
A massive, powerful Central American cichlid famous for its extreme intelligence, interactive 'wet pet' behavior, and intense aggression. Often confused with the Red Devil, the Midas Cichlid is a bulky, earth-eating predator that requires a very large tank, immense filtration, and is notorious for aggressively attacking tank mates, heaters, and even its owner's hands.
Chocolate Cichlid
Hypselecara temporalis
A large, deep-bodied South American cichlid famous for its 'gentle giant' temperament. They undergo significant color changes as they mature, eventually displaying rich chocolate browns, greens, and vibrant reds. Though peaceful for their size, they are still cichlids and will consume any fish small enough to fit in their mouths.
Red Devil Cichlid
Amphilophus labiatus
A massive, extremely aggressive Central American cichlid. Aptly named, the Red Devil is highly intelligent, interactive, and famous for 'glass-banging' at their owners. They are powerful diggers that will uproot plants and rearrange decor. Because of their sheer aggression and jaw strength, they are almost exclusively kept as 'wet pets' in solitary setups.
Uaru
Uaru amphiacanthoides
A large, relatively peaceful but highly gregarious South American cichlid. Often kept with Discus due to their shared need for very warm, pristine, acidic water. They are notorious herbivores that will devour almost any aquatic plant, and they actually require grazing on driftwood for proper digestion. They must be kept in groups.
Blue Tilapia
Oreochromis aureus
A robust, large-growing African cichlid famous for its hardiness, high growth rate, and commercial value. In the aquarium, they are highly active, extremely messy, and will systematically destroy any live plants or intricate hardscape by digging massive crater nests. They are highly adaptable to various water conditions, including brackish water.