Order: the Perciformes
Family: the Chichlidae
Species: Astronotus ocellatus
This portal is dedicated to fish classified as above: Oscar fish.
For some a night mare, that overgrew the tank and murdered all the residents, for the others an aquaristic fascination, compensating all the shortcomings with its behaviour and appearance.
While analysing the fish name - "Astronotus Ocellatus" - we have got: "astrum" - a constellation; "notus" - marked; "Astronotus" - marked with a star (shining spot); "ocellatus" - an eye.
The fish classification changed in a time - the Oscar fish was described as below:
Lobotes ocellatus - Cuvier M S 1829
Astronotus ocellatus - Swaison 1839
Acara crassispinnis - Heckel 1840
Cychla rubroocellata - Schomburgk 1843
Hygrogonus ocellatus - Gunther 1862
Hygrogonus ocellatus - Cope 1871/72
Acara compressus - Cope 1871/72
Acara ocellata - Steindachner 1878
Astronotus ocellatus - Swaison 1882
Acara (Hygrogonus) ocellata - Steindachner 1883
Astronotus ocellatus - Eigenmann - Bray - Pellegrin 1903
Astronotus ocellatus var. zebra - Pellegrin 1903
Astronotus ocellatus - Regan 1905
There are some other species within the Astronotus genus (A. crassipinnis, A. orbiculatus, A. sp. "Wenezuela" - unclassified variety or species), however we will get interested in them only when they appear in our tanks.
Oscars are huge, giving an impression (mistaken!) of being rather slow, sturdy built fish. What calls the attention is a massive body, a large head with a proportional huge mouth and big eyes - the look of the fish is so extremely sharp and that is not easy to state who is the observer, and who is the observed. The soft parts of fins are longer than those with hard rays. They present their beauty when the fish tries to impress - as a warning, during a fight or a courtship.
The standard fish dimensions are stated as following:
The height of the head is 2 to 2,5 times shorter than the length of the thorax.
The eye diameter is 4 to 4,33 times smaller than the length of the head.
The mouth is equal the eye diameter, or longer.
The distance between the eyes is equal 2.25 to 2.33 of the eye diameter.
The mouth is located diagonally.
The lower jaw is slightly protruding.
There are 7-9 lines of scales on the cheeks.
The foremost gill-covers are naked.
D XII-XIV/19-21, AIII/15-16. A dorsal fin starts up with gill chink.
A length of rays in dorsal fin slightly increases backwards. The longest ray measures approx. 0.33 of the length of the head.
Pectoral fins are as long as the head.
The tail-fin is rounded.
A tail base is short. A length of the base is equal 0.4-0.5 of its height.
The lateral line is broken.
Different colour varieties have been bred for aquarium industry, also the shape of the body as well as the lenght of fins have been modified (please read: Oscar varieties.)
The common form is olive-brown colour, with spots of difficult to define colours and individually variable: from black through rotten green to steel-grey blue.
On a tail our attention is attracted by "an eye of a peacock's tail" - a black spot surrounded by orange scales. There are similar orange scales in foremost part of the body, and the number increases with age. Nominally, the fish grow to a length of 35 cm, but specimen longer than 40 cm is not exceptional, with a weight exceeding 1100 g. It lives up to 10-25 years, but sources vary on that subject.
In the wild Oscar fish occurs in the North-West part of Southern America. Its existence is limited to Rio Ucajali and upper course of Amazon river in Peru and Brazil.
Artificially the fish was introduced into waters of Florida, where in Everglades it created a stable population, increasing in number. In the natural environment Oscar fish prefers slow moving water, with a number of submerged trunks, which enable both a shelter and a right place for preying.
The diet of Oscars consists mostly of aquatic and land insects (collected from the surface of water), small fish, crustaceans, shellfish. The attack is quick as lightning: in a moment a slow animal changes itself into predator, rarely missing the aim.
Fish start spawning after they are mated. The sex differences are inconsiderable, estimation based on a size of the body, a size of the adipose hump or coloration is incorrect. It is possible to discern the sex of fish, especially during spawning, looking at the shape and size of genital papillae.
Female lays up to 2000 eggs. Both of the parents protect the eggs, larvae (hatching after 3-4 days, depending on the temperature of water) and free-swimming fry.
The temperature requirements are not considerable - Oscars tolerate a wide range of temperature, with the optimum between 21 and 26 degrees Centigrade. A lethal temperature for Oscars, limiting their distribution is 12.9 degrees Centigrade.
Authors: Rafał Wasiak, Kamil Kielak
AKWARIUM Magazine, LI: 2001, No. (136) 3
Translated by: Dorota Garstka (Bromba)