Astronotus ocellatus is a species of fish from the cichlid family known under a variety of common names, including oscar, tiger oscar, velvet cichlid, or marble cichlid. In South America, where the species naturally resides, A. ocellatus specimens are often found for sale as a food fish in the local markets. The fish can also be found in other areas, including China, Australia, and the United States. It is considered a popular aquarium fish in the U.S. Oscars have been reported to grow to about 45 cm (18 in) in length and 1.6 kilograms (3.5 lb) in weight. The wild-caught forms of the species are typically darkly coloured with yellow-ringed spots or ocelli on the caudal peduncle and on the dorsal fin. These ocelli have been suggested to function to limit fin-nipping by piranha (Serrasalmus spp.), which co-occur with A. ocellatus in its natural environment. The species is also able to rapidly alter its colouration, a trait which facilitates ritualised territorial and combat behaviours amongst conspecifics. Juvenile oscars have a different colouration from adults, and are striped with white and orange wavy bands and have spotted heads. The Oscar is native to Peru, Ecuador, 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 River drainages. In its natural environment, the species typically occurs in slow-moving white-water habitats, and has been observed sheltering under submerged branches.