| Oscar fish | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Cichliformes |
| Family: | Cichlidae |
| Genus: | Astronotus |
| Species: | A. ocellatus |
| Binomial name | |
| Astronotus ocellatus (Agassiz, 1831) | |
Theoscar (Astronotus ocellatus) is a species of fish from thecichlidfamily known under a variety of common names, includingtiger oscar,velvet cichlid, andmarble cichlid.[2] 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.[3][4] The fish has been introduced to other areas, including India, China, Australia, and the United States. It is considered a popularaquarium fish in Europe and the U.S.[5][6][7]
The species was originally described byLouis Agassiz in 1831 asLobotes ocellatus, as he mistakenly believed the species was marine; later work assigned the species to the genusAstronotus.[8] The species also has a number of junior synonyms:Acara compressus,Acara hyposticta,Astronotus ocellatus zebra, andAstronotus orbiculatus.[9]
_(Rio_Negro%2c_Manaos%2c_Brazil).jpg)
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.[2] The wild-caught forms of the species are typically darkly coloured with yellow-ringed spots orocelli on thecaudal peduncle and on thedorsal fin.[6] These ocelli have been suggested to function to limit fin-nipping bypiranha (Serrasalmus spp.), which co-occur withA. ocellatus in its natural environment.[8][10] The species is also able to rapidly alter its colouration, a trait which facilitates ritualised territorial and combat behaviours amongst conspecifics.[11] Juvenile oscars have a different colouration from adults, and are striped with white and orange wavy bands and have spotted heads.[8]
A. ocellatus is native to Brazil, Colombia, Ecuador, Guyana, French Guiana, Suriname, Peru, and Venezuela, and occurs in theAmazon River basin, along theAmazon,Içá,Negro,Solimões, andUcayali River systems, and also in theApprouague andOyapock River drainages.[2][3] In its natural environment, the species typically occurs in slow-movingwhite-water habitats, and has been observed sheltering under submerged branches.[6] Feral populations also occur in China,[12] northern Australia,[13] andFlorida, USA[14] 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).[15]
Although the species is widely regarded assexually monomorphic,[6] males have been suggested to grow more quickly,[citation needed] and in some naturally occurring strains, males are noted to possess dark blotches on the base of their dorsal fins.[7][8] The species reaches sexual maturity around one year of age,[16] and continues to reproduce for 9–10 years.[16] Frequency and timing of spawning may be related to the occurrence of rain.[17]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.[citation needed]. Smaller females lay around 300–500 eggs, while larger female oscars can lay about 2,500-3,000 eggs.[16] Like most cichlids,A. ocellatus practices brood care, although the duration of brood care in the wild remains unknown.[7]
Oscar fish can live in the aquarium with almost any type of fish around the same size as it gets, for example any type of cichlids and predatory fish.[citation needed]
Oscar fish are omnivores.Most fish eaten byA. ocellatus in the wild are relatively sedentarycatfish, includingBunocephalus,Rineloricaria, andOchmacanthus species.[10] The species uses a suction mechanism to capture prey,[18] and has been reported to exhibit "lying-on-side" death mimicry in a similar fashion toParachromis friedrichsthalii andNimbochromis livingstonii.[19][20] Wild oscars also consume shrimp, snails, insects and insect larvae, as well as fruits and nuts on a seasonal basis.[21] The species also has an absolute requirement forvitamin C, and develops health problems in its absence.[22] Captive oscars generally eat fish food designed for large carnivorous fish:crayfish, worms, and insects (such as flies, crickets and grasshoppers).[23]
Oscars will often lay claim to an area of the aquarium and will be very aggressive towards other fish encroaching on their newly establishedterritory 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.[24]
A number of ornamental varieties ofA. ocellatus have been developed for theaquarium industry. These include forms with greater intensity and quantities of red marbling across the body,albino,leucistic, andxanthistic 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.[25] 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 aspainting.[26]
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