Oscar
Astronotus ocellatus
intermediate careOverview
The oscar (Astronotus ocellatus) is a huge-personality cichlid that learns to recognise its keeper, begs at the glass and rearranges the tank to taste. It is also a genuinely large fish — 30 cm or more — that needs a big, well-filtered tank and a long-term commitment measured in decades. Oscars are rewarding for keepers with the space and filtration to match, and a poor choice for anyone hoping they will “stay small”.
Tank & water
Be honest about size from day one. A single oscar needs at least 250 litres (55 gallons), and a pair closer to 400 litres. See our large-tank guide.
- Temperature: 23–28 °C from a robust, well-sized heater.
- Water: pH 6.0–7.5, moderate hardness; test regularly with a kit.
- Powerful filtration: oscars are extremely messy — oversize the filter and keep nitrate down with big water changes.
Feeding
Oscars are carnivores. Feed a quality large-cichlid pellet as the staple, supplemented with frozen or fresh meaty foods such as prawns, mussel and earthworms. Avoid a feeder-fish diet, which risks disease and poor nutrition, and never feed mammalian meat like beef heart as a staple. Big appetites mean big waste, so match feeding with filtration and water changes.
Tankmates
Best kept alone or as a bonded pair. If you want tankmates, choose fish too large to be eaten and tough enough to share space with a boisterous cichlid, in a very large tank — large plecos or comparably sized robust cichlids. Avoid all small, slow or long-finned fish. For stocking a big predator, read how many fish in an aquarium.
Oscar — frequently asked questions
How big do oscars get and how fast?
Oscars grow to 30–35 cm and reach much of that size within the first year — they can add a couple of centimetres a month as juveniles. The cute 5 cm fish in the shop becomes a hand-sized adult fast, so buy the big tank before the fish, not after.
What size tank does an oscar need?
At least 250 litres (about 55–75 gallons) for a single adult, and roughly 400 litres for a pair. Anything smaller stunts them, fouls quickly and shortens their lives. Oscars are big, messy, long-lived fish and the tank size is non-negotiable.
Can oscars live with other fish?
Only carefully. Oscars are predatory and will eat anything they can swallow, so tankmates must be too large to be prey and robust enough to handle an oscar's bulk — think large plecos or similarly sized cichlids in a very big tank. Many keepers house oscars alone or as a bonded pair.
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