Oscars are some of the most popular pet fish because of their character, intelligence and the way they interact with their owners. They are ruled by their bellies - a good characteristic for pet/owner bonding as they’re always hungry and will beg for food, and take an interest in what’s going on outside of their tanks too. But lots of adult Oscars get rehomed, and some get a bum wrap from unscrupulous owners who keep them in cramped tanks with poor water quality, and unnecessary, sometimes gruesome diets.


Hailing from northern and central South America, Oscars occur in a wide range of river, lake and swamp habitats where they cohabit with characins, catfish and other cichlids, and can be found with everything from Angelfish and Discus to Piranha. Escapees have been introduced to other waterways around the world including in Florida, where anglers can often catch them on rod and line.

The ocellatus part of their name Astronotus ocellatus refers to the “eye spot” on their tails, which is a natural defence against fish such as piranhas, which may take a chunk out of the wrong eye, removing some tail fin but leaving the Oscar to swim another day. Until recently Oscars were thought to be monotypic, and the only members of their genus, but A.orbicularis and A. crassipinnis are now also valid, and rarely available sought-after oscar species.


Oscars prefer slow, sluggish or still habitats which are often filled with wood, leaves and plant life, or covered by overhanging vegetation. They like their water to be soft and acidic with a pH of 4-6 in the wild, although generations of tank bred fish seem very tolerant of pH values up to 8. Temperatures can go as low as 20 Celsius, and probably fall that low and lower in Florida, although those wild fish that are in the same lakes as Discus are probably not experiencing temperatures much under 28C.

In the aquarium, 24-28C should make them happy, although at the higher end they will require more food, be more active, and need more oxygen. Young fish may shoal although once they reach maturity Oscars slow down, thin themselves out and live solitary lives when not breeding. They like to hang out in that overhanging vegetation, keeping themselves out of sight from both predators and prey.  


The maximum size for an Oscar is about 12"/30cm, although some old, well looked after specimens in very large tanks may exceed this. Most adult Oscars are considered an adult at about 20-25cm, and it's that size that is the most often seen being offered for rehoming. Juvenile Oscars are available from upwards of 5cm, although they grow rapidly, consuming or outcompeting tank mates and becoming less and less tolerant of their own kind and of any fish which are perceived as a threat to their food source. 

Oscars can’t be sexed, so they need to be able to choose their own mates. Sometimes a group will grow up together with no problems, sometimes a female-female pair will form, but often subadult Oscars fall out, hence the glut of Oscars needing new homes.

Tank setup

At 30cm in length and a few pounds in weight, Oscars are large fish and need a large tank - especially if kept in pairs, groups or with other similarly large fish. Utopia would be a 180x60x60cm tank for a mated pair and considering their longevity of some twenty years, this can be a long term undertaking. Juveniles are kept in tanks upwards of 80cm, although part of the rehoming problem is people not being willing to shell out for a much larger tank when the oscar inevitably grows, and that can be in as short a space of time as one year. 

Filtration should be powerful to cope with their waste. Oscar owners will know that they can eat huge amounts of food, with large crumbs being ejected via the gills at the same time, and large, greedy fish also means lots of large droppings and ammonia. A Fluval FX6 external power filter seems almost purpose-built for Oscars, being oversized in every way, and will cope well. 

Heater(s) should be either tough and in a protected casing, or outside of the aquarium, in a thermofilter or via an inline heater plumbed into the filter tubing. Lighting is usually far brighter than these fish need, but LED spotlights can look particularly effective, especially if recreating that Amazonian rainforest canopy effect. You’ll get the best from your Oscars, and breeding potential, if you keep them in soft water with a low pH. If your tap water is hard, you may want to consider an RO unit. 


Oscar keepers and decorative taste don’t always go hand in hand, so many are kept with coloured gravel and resin ornaments like skulls or shipwrecks. The fish seem fine with this, although if you want to recreate a more authentic piece of the Amazon opt for a black background, fine, inert sand on the bottom and large pieces of bogwood.

There may be some live plants in Oscar habitats but they will destroy them in captivity, another reason why bright light is not necessary, so some poetic licence could be used and a few forest canopy style replica plants, suitable for reptile terraria, may look the part and stand up to being bitten. But a dark, woody tank is all your Oscars need to feel right at home. 


Oscars are often paired up with Common or Sailfin plecos, and for a number of reasons. They grow to a similar size, the armoured catfish are protected from the Oscar, and they are often the only two species which are hardy enough to weather new or poorly maintained, unsuitable aquaria. But Common and Sailfin plecs are very messy too. 

Oscars may be the smallest fish in the tank when housed with Pacu, Arowana and Peacock bass, although then they tend to lose their personality and can often be the least boisterous fish in the tank. Other large South American cichlids like Severums, Uaru and Hoplarchus can work, along with Disc characins, Semaprochilodus and Leporinus.

Large Central American cichlids can be too aggressive even for Oscars, and Pike cichlids do tend to squabble with them over food as they compete in nature. But other large, peaceful species like Synodontis catfish, Tinfoil barbs and hybrid Parrot cichlids are ok if you want something different in the tank with them.

Any small tankmates will be eaten. 


Oscars do eat fish, but they are not obligate piscivores and in nature, they have a surprisingly varied diet including insects, fruits, seeds, and plant matter. The feeding of live fish to Oscars is both unnecessary and against the law in the UK. If you want to offer fish then frozen Lancefish, Whitebait and Smelt are available, along with frozen prawns, cockles and mussels.

But a large stick or pellet aimed at carnivorous tropical fish should make up their staple diet, and ensure that they get all the vitamins that they need. As the fish grow they can be fed less often, perhaps every other day. Especially with meaty foods. 


Oscars can be bred in captivity and are bred in their millions by commercial fish farms, but it's not common in the aquarium, especially when considering just how many Oscars are kept. As mentioned above, adult fish may see each other as competition for food first and foremost so may be difficult to pair off. And all female pairs can also occur. 

There aren’t any sexual differences short of the shape of the vent when the fish are actually spawning, and even if spawning occurs, they may not be fertilised. But good water quality, good diet and a low pH are a good start, along with a long term harmonious, adult pair. Oscars prefer to spawn on a large, flat surface like a slate, so place that on the bottom in the middle of the tank and they may be persuaded. Thousands of eggs will be laid, and the parents will protect the eggs and fry once hatched. 


There are now many Oscar varieties available including albino, tiger, red tiger, red and longfin. Pairs can form from two very different fish and their offspring will then go on to be very different again. This author is a sucker for the wild type Oscars and looks forward to the days when the other two species are more widely available. A south American cichlid tank doesn’t have to just be Geophagus, angels or discus, and a purpose-designed Oscar tank may combine biotope, cichlid, predatory fish, breeding project and pet fish all into one.