The oscar (Astronotus ocellatus) is a species of fish from the cichlid family known under a variety of common names, including Tiger Oscar, Velvet Cichlid, and Marble Cichlid. In tropical 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 has been introduced to other areas, including India, China, Australia, and the United States. It is considered a popular aquarium fish in Europe and the U.S.
Taxonomy
The species was originally described by Louis Agassiz in 1831 as Lobotes ocellatus, as he mistakenly believed the species was marine; later work assigned the species to the genus Astronotus. The species also has a number of junior synonyms: Acara compressus, Acara hyposticta, Astronotus ocellatus zebra, and Astronotus orbiculatus.
Description
thumb|left|Ocelli on dorsal fin and caudal peduncle
alt=watercolor of Astronotus ocellatus|thumb|1831 watercolor of Astronotus ocellatus by [[Jacques Burkhardt.]]
A. ocellatus examples have been reported to grow to about in length and in weight. 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. 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, USA as a byproduct 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 (55.22 °F).
Reproduction
thumb|200px|right|Young Oscar, about 2 in
Although the species is widely regarded as sexually monomorphic, and in some naturally occurring strains, males are noted to possess dark blotches on the base of their dorsal fins. and continues to reproduce for 9–10 years. A. ocellatus fish are biparental substrate spawners, though detailed information regarding their reproduction in the wild is scarce.
In captivity, pairs are known to select and clean generally flattened horizontal or vertical surfaces on which to lay their eggs. Smaller females lay around 300–500 eggs, while larger female oscars can lay about 2,500-3,000 eggs. and has been reported to exhibit "lying-on-side" death mimicry in a similar fashion to Parachromis friedrichsthalii and Nimbochromis livingstonii. Wild oscars also consume shrimp, snails, insects and insect larvae, as well as fruits and nuts on a seasonal basis. The species also has an absolute requirement for vitamin C, and develops health problems in its absence. Captive oscars generally eat fish food designed for large carnivorous fish: crayfish, worms, and insects (such as flies, crickets and grasshoppers).
Territorial behavior
175px|left|thumb|An albino oscar
Oscars will often lay claim to an area of the aquarium and will be very aggressive towards other fish encroaching on their newly established territory inside the aquarium or lake. The size of the territory varies depending on the size and aggressiveness of the fish, and its surroundings. Once the oscar establishes a territory, it will vigorously defend it by chasing away other fish.
Varieties
right|thumb|A [[Leucism|leucistic long-finned oscar]]
A number of ornamental varieties of A. ocellatus 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 the mainly red colouration of the flanks are frequently sold under the trade name of red oscars. The patterning of red pigment differs between individuals. In recent years long-finned varieties have also been developed. The species is also occasionally artificially coloured by a process known as painting.