Oscar

Looks how to spot one

Scaled, deep-bodied cichlid

A big, oval, heavy-set cichlid with a broad head, thick lips and large dark eyes. Wild fish are olive-brown to near black, splashed with orange and red, and carry a bold dark spot ringed in orange near the base of the tail (and often along the dorsal fin). Youngsters look quite different, with wavy white and orange bands and a spotted head.23

Personality what they are like

Confident, curious and territorial. Oscars claim an area and defend it, and they sort themselves into pecking orders using colour changes and side-on or head-on displays rather than constant fighting. For a fish of its size it is not especially quarrelsome, but it is a predator, so anything small enough to fit in its mouth will be seen as food.234

Daily activity how busy a day looks

Active and inquisitive; it likes open swimming space plus a soft sandy bottom, which it digs into when preparing to spawn.41

Grooming and care the hands-on bits

A large, meat-eating fish, so strong filtration and regular partial water changes keep the water clean. Plants and decorations should be sturdy, and the tank should be sized for the adult fish from the start.4

Home where they are happiest

An aquarium of at least about 150 x 60 cm (roughly 540 litres) for an adult. Water 20 to 28 C, pH about 6.0 to 8.0 and hardness roughly 5 to 20 dGH. A soft sand substrate suits its digging habit. It needs warm water year round, as it cannot cope with temperatures below about 13 C.412

Food basics what goes in the bowl

An omnivore that leans heavily towards meaty food. In the wild it eats small fish, crayfish, shrimp, snails, worms, insect larvae and, in season, fallen fruit and nuts. In the aquarium, a good quality cichlid pellet as the staple, topped up with earthworms, shrimp and other frozen or live invertebrates. Its diet should include vitamin C. Mammal or bird meat and live feeder fish are best avoided.421

Company who they like around

Can be kept singly or as a bonded pair. Tankmates must be similar in size and robust, such as larger characins, headstanders, other big cichlids and larger catfish, in a very spacious tank. It is not a fish for a typical community aquarium.4

The story where it all began

The Swiss-born naturalist Louis Agassiz described the oscar in 1831. He first placed it in the genus Lobotes, believing it to be a saltwater fish, before it was recognised as a freshwater cichlid and moved to Astronotus. In its home range the oscar has long been caught and sold in local markets as a food fish. During the twentieth century it became a favourite of aquarium keepers, and breeders developed many ornamental forms such as tiger, red, albino and long-finned oscars. Fish that escaped or were released from the ornamental trade now live wild in warm places outside South America, including Florida, northern Australia and parts of China, and in Florida it is also targeted by anglers as a game fish. Because it shows clear, measurable social behaviour, the oscar is also a common subject in scientific studies of behaviour and development.231

Recognised by the official bits

IUCN Red List

Assessed as Least Concern (November 2020)1

Taxonomy

Family Cichlidae; genetic studies suggest the genus Astronotus may hold further, not yet described species4