By Lance Griffioen
Geographic Range
These fish are found in the Amazon River basin, from the Orinoco River to the Rio Paraguay, throughout Venezuela, Guyana, and Paraguay. (The Aquarium Encyclopedia, 1983.)
Biogeographic Regions:
neotropical 
(native ).
Habitat
Found in the tropical lowlands of South America, A. ocellatus prefers the floodplains and swamps of the Amazon River basin. They are most comfortable in water about 25 degrees Celsius, or slightly higher for breeding. (Kullander, 1996)
Aquatic Biomes:
rivers and streams.
Physical Description
(4.4 to 8.8 lbs)
Compared to other fishes, Astronotus ocellatus has a slender, laterally compressed body, and a blunt head with a large mouth and protruding jaw. Colors vary greatly among geographic regions and individuals, but most are dark green to black, with red stripes along its back and a red circle on the base of the tail fin. The adult fish grows up to 35 cm long. Males and females are visually indistinguishable. (Gracyalny, 1996.)
Some key physical features:
bilateral symmetry .
Reproduction
Though they can become much larger, A. ocellatus are sexually mature soon in life, usually by the time they are 12 cm long. These fish exhibit a high degree of parental care. After spawning in open water, the eggs are laid on a piece of ground that has been cleared by one of the parents. After three or four days, the eggs hatch. The brood is then transported to a sandy hollow for about one week. Young fish have been observed clinging to their parents with their mouths, even after they are able to swim freely. (The Aquarium Encyclopedia, 1983)
Behavior
In captivity, A. ocellatus is one of the most popular freshwater aquarium fishes, largely because of its coloring and distinguishing personalities. They are said to be able to recognize their owners from other people, and can even be trained to perform simple tricks for food, like jumping out of the water. Astronotus ocellatus, like many Cichlids, often exhibit changes in color darkness. The rapid lightening of color is thought to be an expression of fear, as it is often displayed while being attacked by predators or other Oscars. Alternatively, it may serve to make the visual borders of the fish itself harder to see, thus protecting it from potential attackers. (Gracyalny, 1996, Beeching, 1995)
Key behaviors:
natatorial ; motile .
Food Habits
Although these predators are not at all choosy, they feed mostly on insect larvae and smaller fish. Their feeding habits require that Oscars have excellent eyesight. Because of this, they have been the subject of numerous studies concerning eyesight in fish. (The Aquarium Encyclopedia, 1983, Andison and Sivak, 1996)
Economic Importance for Humans: Positive
As a popular aquarium fish, A ocellatus has some obvious economic importance to humans. Additionally, it has been used by biologists in numerous studies of fish, including studies on behavior, eyesight, auditory systems, and swim bladders.
Conservation Status
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For More Information
Find Astronotus ocellatus information at
Contributors
Lance Griffioen (author), University of Michigan.
