Astronotus ocellatus is a species of fish from the cichlid family known under a variety of common names including Oscar Cichlid, Tiger Oscar, Velvet Cichlid or Marble Cichlid. In South America, where the species occurs, Oscars are often found for sale as a food fish in the local markets, however, its slow growth limits its potential for aquaculture. The species is also a very popular aquarium fish.

Oscars have been reported to grow to a length of 45 cm (18 in) and a mass of 1.6 kg (3.5 lb). The wild caught forms of the species are typically darkly colored with orange ringed-spots or ocelli on the caudal peduncle and on the dorsal fin. It has been suggested that these ocelli function to limit fin-nipping by piranha which co-occur with oscars in its natural environment. Further studies have suggested the ocelli may also be important for intra-specific communication. The species is also able to rapidly alter its coloration, a trait which facilitates ritualized territorial and combat behaviors amongst co specifics. Juvenile oscars have a different coloration to adults and are striped with white and orange wavy bands and have spotted heads.

Oscar Cichlids are native to Peru, Colombia, Brazil and French Guiana and occurs in the Amazon river basin, along the Amazonas, Içá, Negro, Solimões and Ucayali river systems, and also in the Approuague and Oyapock drainages. In its natural environment the species typically occurs in slow moving white-water habitats, and has been observed sheltering under submerged branches. Feral populations also occur in China, northern Australia, and Florida, as a by-product of the ornamental fish trade. The species is limited in its distribution by its intolerance of cooler water temperatures, the lower lethal limit for the species is 12.9 °C (55.2 °F).

A number of ornamental varieties of oscars have been developed for the aquarium industry. These include forms with greater intensity and quantities of red marbling across the body, albino, leucistic and xanthistic forms. A. ocellatus with marbled patches of red pigmentation are sold as red tiger oscars, while those strains with mainly red coloration of the flanks are frequently sold under the trade name of red oscars. In recent years long-finned varieties have also been developed. The species is also occasionally artificially colored by a process known as painting.

Oscar Cichlid's are popular as pets, and are regarded as intelligent by aquarists. This is in part as they learn to associate their owners and food and are purported to be able to distinguish their owner from strangers. Despite their large size, and predatory nature oscars are relatively placid aquarium residents best housed with other fishes too large to be considered food items. Oscars are known to uproot plants, and move other objects in aquariums and are best maintained in volumes of 200-600 liters (52-158 gallon)s. Oscars are relatively tolerant of a range of typical aquarium water chemistries, though its large size and messy feeding habitats necessitates efficient filtration be installed on the aquarium. Oscars are undemanding to feed in captivity and will accept a range of foods that include pieces of fish and prepared cichlid foods.