Original description: Cuvier 1829 in Spix and Agassiz, Selecta genera at species Pisc.Bras, p129, p168, PI.F,1829.
Common name: Oscar or Velvet Cichlid or Marbled Cichlid
Distribution: Very widely distributed throughout South America, in the northern central parts and in the northern central parts and in particular the whole length of the Amazon River and many of its tributaries, and in the Rio Negro in Brazil.
Size: Males will grow to around 16" (40cm) in aquariums that allow them to reach this size, with females being around 13"/14" (33/35cm) total length.

This species has been in the hobby for quite a long time and will be around a lot longer than most of us. It cannot be kept with smal fish as it will be merciless and devour them. However, with fish of its own kind (e.g. other cichlids) it will get along quite well in general. You can get rogues in any fish family and this will sometimes happen with Oscars, but in general they are rather harmless. This species, even though it will eat anything small enough to get into its mouth, is easily bullied by more robust species like Black Belts, Dovii, Managuense, etc. For a fish that grows as large as the Oscar, it certainly gives in quickly when other larger fish start "picking on them".

The Oscar will tolerate a wide variety of water conditions provided that it is not too extreme. I have seen oscars in a pH of 3.8 and their fins are as ragged as you could ever see. simply because they were in such pathetic conditions. By bringing them back to a much more realistic pH the fins all return to normal, and the frayed look soon disappears. You must realise that any extreme in water conditions will bring on stress and this can sometimes lead to other problems such as "hole-in-the-head".

Oscars prefer a pH of just under 7.0 and 6.5-6.8 and slightly soft water conditions. I have had them in water which has been hard and very alkaline as well as in soft and acidic water conditions and they seem to prefer the latter. For your information, according to Shafland and Pestrak (Env.Biol.Fish. 7 (2) pp 149 -156) the Oscar was recorded to reduce feeding at 17.1 degrees C, stopped feeding at 14.5 degrees C. became listless at 13.6 and lost equilibrium and then died at 12.9 degrees C.

Oscars will eat just about anything offered to them. Some foods they seem to relish are beefheart (fed sparingly), tubifex worms, earth worms (washed), pellets (both floating and sinking types), flake foods, live fish (Gambusia), freeze-dried such as river shrimps, krill, tubifex worms, etc. as well as all types of frozen foods, e.g. blood worms, squid, mussel, prawns and even frozen green peas.

As far as the food which should be fed to Oscars, too many people seem to be feeding beefheart exclusively without alternating the diet. Although there is no real evidence, I believe this to be detrimental to the fish.

I do not believe it when many people who keep Oscars tell me that their particular fish only like beefheart or a certain kind of pellet. I have discounted this when a customer once lent me her Oscar which, up until that time, had only live foods and frozen meat; I told her I would get it to eat flake food. It took around three weeks for the Oscar to respond and eventually eat flakes as the fish will coerce its owner into doing what it wants you to do, and will refuse to eat anything else. Initially, this Oscar refused to eat all the flakes I offered it, and consequently I had to remove all the uneaten food otherwise it would have fouled the water and the fish might have suffered accordingly. However, after going almost three weeks without any sustenance, the Oscar finally took the flakes offered. It has not shown any noticeable loss of weight in this time, but it did prove my theory that any fish can coerce its owner into feeding it what it likes most.

However, feeding a substance like beefheart as a sole source of food is, I believe, silly. In nature this fish does not get beefheart every day of the week, so it should not be fed as a mojor food source in the aquarium. Beefheart is desirale for growth of a fish like the Oscar but should only be fed once or twice a week; the rest of the time it should be fed alternative foods such as pellets (floating and sinking types), freeze-dried food and foods such as prawn, squid, bloodworms, green peas, flakes, krill and, of course, an energy source like live fish such as Gambusia affinis (Mosquitofish). By doing this, the Oscar is not reliant on one food source, and will not suddenly stop eating food - much to their owner's anxiety.

Another reason I believe beefheart should not be a mojor part of the diet is because it creates problems with the fish's digestive system and can cause "hole-in-the-head" disease, which is common in Oscars. Although I cannot prove this, I have found that a great number of fish which develop this desease have been fed diets largely made up of meat such as beefheart. Another factor contributing to my supposition is that the disease is caused by an internal parasitic infestation of the gut region of the fish. In time, these parasites multiply to saturate the gut, evenentually breaking out through its wall and into the bloodstram. Here they work their way through the blood vessels and into the soft tissue of the head region, hence the "hole-in-the-head". Only by limiting the quantity of meaty foods fed to Oscars will this problem lessen its incidence, simply because the fish cannot digest all this meat into his system.

Oscars are not usually territorial, except when they want to spawn, but this is the same with most cichlids anyway. Having spawned this species successfully, I can advise that they require the water very warm at 29-31 degrees C, and a pH of around 6.5-6.7 plus slight water softness at around 50-70PPM. If you duplicate these conditions you should succeed in spawning Oscars.

The only major problem that is faced by most people is obtaining a compatible pair suitable for spawning, as I have seen quite a lot of supposed pairs which turn out to be two females. This happens quite a lot as ther is no sure way of sexing Oscars. However, I use a method which involves the identification of fins in fullygrown (10" or 25cm) fish to identify sexes. Males have much longer anal and dorsal fins which seem to overlap the caudal fin. Females appear to me to have a noticeable "gap" in between the anal fin and caudal fin when fully erect. There is also a gap between the dorsal and caudal in some individuals, but this is not always reliable. I find the anal and caudal fins to be the better method of identification. Of course, when they are able to spawn, it becomes obvious which is the female, as ther ovipositor is that much "blunter" than that of the male's, which is slightly bent and pointed.

The other usual way of sexing large cichids, i.e. turning them upside-down to view their breeding apparatus, does not work too well with an Oscar due to the enormous amount of slime that they exude when this method is tried. There are those who stand by other methods of sexing such as observing the colour of gill cheeks, but I believe these to be unreliable; the above method is the one I have found the most accurate.

Once a pair has been selected, either at random by the owner or by the fish themselves in a tank, a spawning pattern develops where the two fish circle each other constantly. They will lock jaws aggressively, sometimes for great lengths of time to prove, it seems, that they are compativle. At the same time they spread their fins and exhibit extraordinary and rapid colour changes, and slap each other with fins and body when preparing to spawn. Having laid a batch of eggs, you will not be able to put your hands anywhere near the fish or their eggs; other fish are also barred from the area.

If the temperature is maintained to the levels already mentioned above the eggs will hatch within 48 hours and become free-swimming some four to five days later. At this stage they shoud be fed on newly hatched and washed (of salt) brine shrimp.

Fry grow rapidly on this source of food, to a point where they have to be coaxed into eating finely grated dry foods, like Mikropan or some other form of fine food. It will not be too long before the fry begin eating adult brine shrimp, daphnia and mosquito larvae plus other suitable foods.

As they grow you will need to keep a close eye on the younsters, as they will begin to prey on their siblings and you will need to separate the different sizes in order to save the maximum number of fish. However, if any are deformed in any way they should be fed to other fish for food as I believe that what happens in nature should also apply in captivity.

Be prepared to make ample water changes for the fry, otherwise stunting may occur, especially if it is a large spawn. Large Oscars can have upwards of 2000 fry at a time, so water changes of at leat 20 per cents weekly should be made to enable the fry to grow uniformly.

Information contributed by:
Norm Halliwell