Definitive guide to Oscars

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You may have thought there was only one Oscar but, as Heiko Bleher explains, there are more species of these popular cichlids than many people realise.

No one really knows when the English name 'Oscar' was first used for the South American cichlid Astronotus ocellatus.

In Germany this fish is called Pfauenaugenbuntbarsch, meaning Peacock cichlid. Some also call it the Marbled or Velvet cichlid. I can only presume that Oscar was coined as a corruption or simplification of its scientific generic name. However, the name has definitely stuck.

The first live specimens were imported in 1929 by the German firm Scholze and Plötzschke. Wilhelm Preatorius collected them live in 1928, probably in the Santarém region of the Amazon.

The earliest captive breeding of Oscars took place in 1933 in the USA and in 1934 in Germany.

Astronotus grow to 35cm/14" and I’ve found them from the upper Amazon down to the Rio Tocantins and in almost every tributary in the Paraguay basin into Paraguay.

I’ve also found what I believe is a complete different species in the Orinoco basin — and in the Guyanas it only lives naturally in Suriname and French Guyana.

The genus Astronotus was first described as a subgenus of Crenilabrus by W Swainson in 1839 and the first species later placed into this genus was collected before 1820 by the Germans P F von Martius and J B de Spix and published in Selecta Genera et Species Piscum 1829 as Lobotes ocellatus (the original drawing of the type species is pictured above).

The pair collected it in the Amazon in a habitat then described as Oceano Atlantico at a time in history when the lower part of the Amazon was referred to as Mar — meaning ocean — as a result of Orellana’s Amazon journey in 1541-1542.

I also found that M E Bloch, a scientist born near my birthplace of Frankfurt in Germany, published between 1782 and 1795 Allgemeine Naturgeschichte der Fische  — a multi-volume work on fishes in which he describes a fish named Holocentrus surinamensis, from Surinam.

This is a brackish and marine species and I found it in several parts of South America in pure freshwater lakes, although it has an almost circum-tropical marine distribution. This is extremely similar to the described Lobotes ocellatus, Agassiz in Spix and Agassiz, 1829.

In 1829-1830 the French naturalist Baron Georges Cuvier wrote about ‘Les Lobotes’ and discussed the new specimens from Martius and Spix, as well as material from M Levaillant collected south of Surinam, specimens from naturalist M. Le Luc de Rivoli collected in Brazil and Bloch’s material, as well as Lobotes from other parts.

Because Bloch’s Surinam specimens looked so much like the other material gathered the baron assigned all specimens to Lobotes ocellatus, possibly also because of the same type locality of Oceano Atlantico.

Both species were later separated again and into two families — Lobotidae for H. surinamensis and Cichlidae for Astronotus. They also have, apart from similar morphology, two to three faint small ocellus near or along the base of their dorsal fin. In the Astronotus ocellatus form from Surinam, as well as in Lobotes surinamensis, these spots are very faint.

Although present in all forms of Astronotus, the caudal ocellus is absent in H. surinamensis.

Swainson wrote in 1839: "The strong analogical resemblance of this sub-genus (Astronotus) to Lobotes deceived Spix and Agassiz into supposing that it really belonged to that genus, hence I am led to suppose it may have the pre-opercule crenated, which some forms definitely have. The lateral line, and many other characters, leave, however, little doubt of belonging to this sub-family".

What was not clear is that the species should take the generic, or rather subgeneric name Astronotus and the type designated Lobotes ocellatus. Later additional species were described and eventually placed into the genus Astronotus (see below).

All had been synonymised into the single species of Astronotus ocellatus until Sven O Kullander in 1986 re-erected A. crassipinnis and wrote: "The species (which I think is a different species) is reported from the Orinoco drainage and numerous localities in the Amazon basin, but apparently several species are confused under the name and names in the synonymy may represent valid species." 

I’m sure there are many species. I have found at least seven different forms, with its largest diversification throughout the Amazon basin in the Purus region where I found six different ones — of which probably only one is A. ocellatus. Some had amazing colours and a completely different morphology from the type:

Astronotus sp.1, Rio Itaparana, Purus region.

Astronotus sp. 2, Rio Itaparana, Purus region.

Astronotus sp. 3, Lagos Solitario, Rio Itaparana, Purus region.

Astronotus sp. 4, Lago UauacÃ, Purus region.

Astronotus sp. 5, Lago Paricatuba, Purus basin.

Astronotus sp. 6, Rio Araguaia, Aruana, Goias, Brazil (picture by J. Mendes).

Astronotus sp. 7, Rio Apure, Venezuela (picture by H. Koepke).

Other forms of Oscars

Since the 1930s, and especially in light of the ornamental fish boom in the latter part of the 20th century, many different colours and forms of Oscars have been produced.

First there was the Red tiger, similar to the wild form but with irregular red markings. This was selectively bred to produce the red form, in which the sides were almost entirely red.

Later came the albinos which were crossed back to the red form to produce marbled and red albinos and an almost endless variety of others.

Later, mutants appeared — which in the wild would have no chance of survival – including long-finned Oscars, resembling Veiltail goldfish.

An endless variety of forms and shapes have been continuously refined into the most horrendous shapes and forms.

Later additions to Astronotus

After Swainson’s observations in 1839, more species were described and added to the genus.

In 1840 there was Heckel’s Acara crassispinnis, from the Natterer collection, together with the first Discus and several other Cichlidae from the Rio Guaporé.

In 1843 there appeared a drawing of a species named Cycla rubro-ocellata by Jardine and Schomburgk in Schomburgk 1843, which was found in the Rio Negro and tributaries and later also placed in Astronotus.

In 1872 there was Cope’s Acara compressus from the Río Ambyiacu, Peru, and in 1978 he described another: Acara hyposticta, also from Peru.

Pellegrin described a subspecies in 1904 as Astronotus ocellatus var. zebra from Santarém, Amazon rver, Pará, Brazil (together with the Symphysodon discus var. aequifasciatus, the Green Discus); and Haseman described the last species in 1911 as Astronotus orbiculatus from Santarém, Amazon river, Pará, Brazil.

Species of the genus

Today’s recognised species are:

Astronotus ocellatus, Agassiz L, in Spix and Agassiz 1829, found from the Orinoco basin, in Surinam and French Guyana south to the Paraguay basin, but this distribution includes several species.

Astronotus crassipinnis, Heckel J J 1840, known from the Río Paraguay, Villa Maria and Caiçara, Río Guaporé near Mato Grosso. Kullander reported it from the upper Amazon in Peru and I found it there, in the Jutaí, Purus basin and elsewhere.

The species and subspecies described below are today considered synonyms of A. ocellatus:

Astronotus compressus,

(Cope E D, 1872) from the Río Ambyiacu, Peru.

Astronotus hyposticta,

(Cope E D, 1878) from the type locality in Peru.

Astronotus orbiculatus, (Haseman J D, 1911) from Santarém, Amazon, Pará. Brazil.

Astronotus rubroocellata, (Jardine W and Schomburgk R H in Schomburgk 1843) from the Rio Negro and tributaries.

Astronotus ocellatus var. zebra (Pellegrin J, 1904) from Santarém, Amazon river, Pará. Brazil.

How can I keep them?

Don’t confine these fishes to a small aquarium. They should have a home which has an absolute minimum length of 120cm/48” —  and the bigger the better as they grow to 35cm/14” very quickly.

As for décor use sand, gravel, rocks and well soaked driftwood, and if you want to risk plants go for robust species like large Echinodorus bleherae and Spatiphyllum. Ceratopteris cornuta is good and you could possibly add some Philodendron on top so the roots can grow into the aquarium, simulating Astronotus’ natural habitat.

Floating plants, such as Eichhornia crassipes, Pistia stratoites or Salvinia species, can also be included.

I would prefer to see Astronotus kept in pairs rather than alone.

Have only largish fishes as tank mates, similar in size to the Astronotus. It’s not that they prey on fishes, but smaller ones might be swallowed. Large catfishes such as Loricaria, Acanthodoras, Pterygoplichthys, Pseudacanthicus and Parancistrus would make good companions.

Regular water changes are important. I suggest 20-30% each week and the more the better. As for water parameters, Astronotus are robust cichlids that are used to water just below pH 7. Temperature should be between 24-30°C/75-86°F.

As for spawning them, I was amazed to see how one Discus establishment in Bangkok breeds Oscars. The owner had built large concrete vats and in each of four small, separate compartments had single entrances, like rooms (see picture below).

Then he placed an equal number of both sexes in the open space and each male would then choose and guide his selected female into one of the ‘rooms’ to mate in their beds, which were just pieces of black slate.

This must be the first fish bordello, but it works, and in every room I saw spawning!

How do I feed these fish?

In nature, Oscars often feed along the surface of the water, taking terrestrial and arboreal arthropods, including Isoptera, Diptera and Ephemetroptera (mayflies and dayflies). Aquatic invertebrates, such as Rotifera (rotifers), Cladocera (water fleas) and Copepoda are frequently eaten too. Oscars also enjoy small fish and take some Amazonian fruits and seeds.

In the aquarium feed them a variety of foods and remember that as they grow they will need bigger food items, like large tablets and granules, lean fish meat, mussels and bloodworms. A friend of mine even gave his tiny tomatoes!

Food-wise, Oscars are generally easy to please.

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