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.
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.
A. ocellatus examples 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.
Distribution and habitat
A. ocellatus is native to Peru, Ecuador, Amazon, Brazil, and French Guiana, and occurs in the Amazon River basin, along the Amazon, 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. 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).
Although the species is widely regarded as sexually monomorphic, males have been suggested to grow more quickly, and in some naturally occurring strains, males are noted to possess dark blotches on the base of their dorsal fins. The species reaches sexual maturity around one year of age, and continues to reproduce for 9–10 years. Frequency and timing of spawning may be related to the occurrence of rain. 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. Like most cichlids, A. ocellatus practices brood care, although the duration of brood care in the wild remains unknown.
In the aquarium
The oscar is one of the most popular cichlids in the aquarium hobby.
Most fish eaten by A. ocellatus in the wild are relatively sedentary catfish, including Bunocephalus, Rineloricaria, and Ochmacanthus species. The species uses a suction mechanism to capture prey, and has been reported to exhibit "laying-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).
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 based on its surroundings. Once the oscar establishes a territory, it will vigorously defend it by chasing away other fish.
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.
- Froese, R. and D. Pauly. Editors. "Astronotus ocellatus, Oscar". FishBase. Archived from the original on 2007-09-29. Retrieved 2007-03-16.
- Kullander SO. "Cichlids: Astronotus ocellatus". Swedish Museum of Natural History. Retrieved 2007-03-16.
- Kohler, CC; et al. "Aquaculture Crsp 22nd Annual Technical Report" (PDF). Oregon State University, USA. Retrieved 2007-03-16.
- Keith, P. O-Y. Le Bail & P. Planquette, (2000) Atlas des poissons d'eau douce de Guyane (tome 2, fascicule I). Publications scientifiques du Muséum national d'Histoire naturelle, Paris, France. p. 286
- Staeck, Wolfgang; Linke, Horst (1995). American Cichlids II: Large Cichlids: A Handbook for Their Identification, Care, and Breeding. Germany: Tetra Press. ISBN 978-1-56465-169-3.
- Loiselle, Paul V. (1995). The Cichlid Aquarium. Germany: Tetra Press. ISBN 978-1-56465-146-4.
- Robert H. Robins. "Oscar". Florida Museum of Natural History. Archived from the original on 2007-03-05. Retrieved 2007-03-18.
- Froese, R. and D. Pauly. Editors. "Synonyms of Astronotus ocellatus". FishBase. Archived from the original on September 29, 2007. Retrieved 2007-03-21.
- Winemiller KO (1990). "Caudal eye spots as deterrents against fin predation in the neotropical cichlid Astronotus ocellatus" (PDF). Copeia. 3 (3): 665–673. doi:10.2307/1446432. JSTOR 1446432. Archived from the original (PDF) on 2012-05-04.
- Beeching, SC (1995). "Colour pattern and inhibition of aggression in the cichlid fish Astronotus ocellatus". Journal of Fish Biology. 47: 50–58. doi:10.1111/j.1095-8649.1995.tb01872.x.
- Ma, X.; Bangxi, X.; Yindong, W. & Mingxue, W. (2003). "Intentionally Introduced and Transferred Fishes in China's Inland Waters". Asian Fisheries Science. 16: 279–290.
- Department of primary industry and fisheries. "Noxious fish – species information". Queensland Government, Australia. Archived from the original on 2007-08-29. Retrieved 2007-03-16.
- United States Geological Survey. "NAS – Species FactSheet Astronotus ocellatus (Agassiz 1831)". United States Government. Archived from the original on 2007-05-02. Retrieved 2007-03-17.
- Shafland, P. L. & J. M. Pestrak (1982). "Lower lethal temperatures for fourteen non-native fishes in Florida". Environmental Biology of Fishes. 7 (2): 139–156. doi:10.1007/BF00001785.
- Dowdy, Meredith. "Astronotus ocellatus Marble cichlid (Also: Red oscar; Velvet cichlid)". animaldiversity.org. University of Michigan Museum of Zoology. Retrieved 11 September 2020.
- Pinto Paiva, M & Nepomuceno, FH (1989). "On the reproduction in captivity of the oscar, Astronotus ocellatus (Cuvier), according to the mating methods (Pisces – Cichlidae)". Amazoniana. 10: 361–377.
- Waltzek,TB and Wainwright, PC (2003). "Functional morphology of extreme jaw protrusion in Neotropical cichlids". Journal of Morphology. 257 (1): 96–106. doi:10.1002/jmor.10111. PMID 12740901.CS1 maint: multiple names: authors list (link)
- Tobler, M. (2005). "Feigning death in the Central American cichlid Parachromis friedrichsthalii". Journal of Fish Biology. 66 (3): 877–881. doi:10.1111/j.0022-1112.2005.00648.x.
- Gibran,FZ. (2004). Armbruster, J. W. (ed.). "Dying or illness feigning: An unreported feeding tactic of the Comb grouper Mycteroperca acutirostris (Serranidae) from the Southwest Atlantic". Copeia. 2004 (2): 403–405. doi:10.1643/CI-03-200R1. JSTOR 1448579.
- "Feeding Oscars in the Home Aquarium". Tropical Fish Hobbyist. June 2007.
- Fracalossi, DM; Allen, ME; Nicholsdagger, DK & Oftedal, OT (1998). "Oscars, Astronotus ocellatus, Have a Dietary Requirement for Vitamin C". The Journal of Nutrition. 128 (10): 1745–1751. doi:10.1093/jn/128.10.1745. PMID 9772145.
- "Oscar Fish Diet". Retrieved 31 Jan 2019.
- Zaret, Thomas (June 1980). "Life History and Growth Relationships of Cichla ocellaris, a Predatory South American Cichlid". Biotropica. Association for Tropical Biology and Conservation. 12 (2): 144–157. doi:10.2307/2387730. JSTOR 2387730.
- Sandford, Gina; Crow, Richard (1991). The Manual of Tank Busters. USA: Tetra Press. ISBN 978-3-89356-041-7.
- Mike Giangrasso. "Death by Dyeing – dyed fish list". Death by Dyeing.org. Retrieved 2007-03-18.
|Wikispecies has information related to Astronotus ocellatus.|
|Wikimedia Commons has media related to Astronotus ocellatus.|