Oscar
Astronotus ocellatus
Cichlidae
About
The Oscar is a large, intelligent cichlid from the slow, warm waters of the western Amazon and Orinoco basins, where it hunts among mud- and sand-bottomed pools and flooded margins. Reaching 30-38 cm and living well over a decade, it is a heavy-bodied predator that swallows any fish small enough to fit its wide mouth, and it constantly digs, uproots plants and rearranges its surroundings. Its personality and habit of recognising its keeper make it a hobby favourite, but it is very commonly mis-kept and quickly outgrows undersized tanks.
Care
Give a single Oscar (or a bonded pair) a large, long tank with a base of at least 150 cm (about 450 L) with powerful, over-rated filtration and weekly 30-50% water changes to handle its huge bioload. Use a secure lid, sand substrate and robust decor. House only with similarly large, non-bite-sized tankmates.
Diet
Predatory omnivore that eats fish, crustaceans and insects in the wild. Staple on a quality cichlid pellet plus earthworms, prawns, mussel and whitefish; skip feeder fish and mammal meat, and control portions to protect water quality.
Tankmate compatibility
Avoid (271)
Computed by the AquaSage engine for a spacious reference tank — always check the full verdict for your exact setup in the calculator.
Full tank-mates guide with reasons →Telling males from females
What works for this species, most reliable first.
- Extended finsStrong · from about 8 months, and later in a suppressed male
On many cichlids and killifish the male's dorsal and anal fins draw out into trailing points as he matures, while the female's stay rounded.
- VentingA hint only · only on a mature fish, easiest when she is in breeding condition
The method breeders use when the answer has to be right. Hold the fish upside down in a wet hand or soft net and look at the two openings ahead of the anal fin. The forward one is the anus; the one behind it is what you are reading.
- Adult sizeA hint only · only across animals of the same age
In many cichlids, catfish and loaches one sex simply grows larger — usually the male, though there are well-known reversals.
Frequently asked questions
- What tank size does a Oscar need?
- A Oscar needs an aquarium of at least 450 litres (118.9 US gallons) with a footprint at least 150 cm (59.1 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Oscar need?
- Oscar does best at 22–30 °C (71.6–86 °F), pH 6–8 and a general hardness of 5–20 °dGH.
- Is the Oscar suitable for beginners?
- Oscar is a demanding species best attempted with some experience — it needs stable, closely watched conditions to thrive.