If you have both a mature male, and female, and a big enough tank, it isn't too hard to get Oscars to spawn. The hardest part of spawning Oscars, is ensuring that you have a pair, and giving them enough space.
Standard practice for obtaining a breeding pair of substrate spawning cichlids is to obtain six juveniles, and allow them to select a mate. This is certainly feasible, but Oscar's don't begin spawning too often before they are six inches, so you'll need a very large tank to house these fish. A 180 gallon would be ideal for such a venture.
Some people would prefer to choose mature Oscar's to breed with. Unfortunately, determining the gender of an Oscar based upon finnage, colouration, markings, behaviour or size are not very reliable.
The only reliable method of determining the gender of an Oscar, is by netting them out of the tank, and holding them still while examining their genital area with a bright light available. It does take some practice to tell the difference, but the male's spawning tube points back towards the tail, and is located just in front of the opening of the anus. The female on the other hand, has a spawning tube that is less pointed, and points straight down. The female's genital area gives the impression of two openings including the anus.
If you choose to try and mate a pair of fish, adding in a divider until they become used to each other is a common tactic. Signs that your Oscar is preparing for spawning activity include such rituals as jaw-locking, tail-slapping, chasing, nipping, posturing, nudging, and rolling over. For some fish in consists of all of these activities to the full range of very few of these behaviours. This "foreplay" can last anywhere from a over a day, to just a few minutes, with periods in between where the Oscars will busily clean the spawning site, which could mean cleaning a rock, or removal of vast quantities of gravel.
Once the Oscars get down to spawning, the eggs are laid in strings, or rows that generally follow a round pattern. The arrangement of the eggs is not particularly orderly, though eggs will not be laid on top of each other. The breeding process will not be completed in one go, with several breaks taking place.
Oscars will lay between several hundred to several
thousand eggs for a large mature female. The Oscars will fan the
eggs, to oxygenate them, and to prevent sediment from being deposited
on them. Oscars are also known to mouth the eggs, and remove unfertilized
eggs. The eggs normally hatch within a day and a half, and the
new fry are generally quite clumsy and unable to do much more
then dart around. If you keep the fry in with the parents, you
might want to put a sponge over the filter intake, as the fry
are apt to be sucked into the filter.
Freshly hatched Oscars can be fed Live Baby Brine shrimp at first, and as they grow you can add in other foods such as baby mosquito larvae, crushed flake and pellet.
Tank Size and decorations for properly maintaining Oscars
As we've discussed, Oscars will easily grow over 12" if kept properly. It seems prudent that one should house a fish in an aquarium where they can turn around, without touching both the front and the back of an aquarium. As such, the minimum recommended size to keep a single Oscar properly, would be a 65/75 gallon aquarium. In keeping two or more Oscars together, the issues include room to hide from aggressive tank mates, and enough water to dilute the large amounts of waste that an Oscar produces. I would suggest that a 100 gallon aquarium is a good starting point, and will admit that the nicest Oscars I have seen were usually in 180 gallon tanks.
When it comes to decorating your aquarium, there is one major item that needs to be part of the plans. Oscars like to rearrange their tanks, so both the appearance of the aquarium, and the safety of your fish must be taken into consideration. An Oscar will dig, will pick up anything it can, and is known to ram what it can pick up against other objects. So with this in mind, don't put in sharp objects, or things that could easily break. In the wild, Oscars will only bother plants that are in their spawning territory. In the aquarium, the same is true usually, but the size of the natural territory of an Oscar is such that you would need a 500 gallon aquarium for the plants to typically be safe.
Large rocks and pieces of driftwood often dominate the aquascaping of the average Oscar aquarium, and can make for an interesting, useful, and safe environment for your Oscar. If you house multiple Oscars, do provide some shelter so that if a fish is being bullied, they can escape the attentions of the bully.
The Substrate, or gravel is really up to the owners preference, but do keep in mind that the larger the gravel, the easier it will be for debris to become trapped in, leading to potential deterioration of the water quality.
Tank mates for Oscars
An Oscar deserves to be the centre piece of an aquarium, and in choosing its tank mates, this must be kept in mind. Oscars can be bullies, so very passive fish should not be included. On the other hand, Oscars really aren't that tough, so many of the more aggressive species shouldn't be considered either. Oscars have a big appetite, and a big mouth, so keeping fish that they can't swallow or can't catch should be considered. Often people will keep Oscars with such fish as Tinfoil Barbs, Silver Dollars, Firemouth Cichlids (Thorichthys meeki), Severums (Heros severus), Pimodella catfish, Synodontis catfish and various "Pleco's" and large loaches.
I've seen some very nice tanks with single Jack Dempseys and Texas Cichlids added in. These fish should be smaller then your Oscar though, as typically they are more aggressive then an Oscar and if they were the same size, or larger, they would likely bully the Oscar.
I've also seen a couple of nice tanks with larger schooling fish, Jumbo Danios and very large Rainbow fish. Even large examples of these fish could become food for Oscar's, so this mix is going to be hit and miss depending on your Oscar, but is spectacular when accomplished.
Below is a listing of some of the variants of Oscars.
Green Oscar - This is the natural occurring colour strain of Oscars.
Red Oscar - Developed by Charoen Pattabonge, a Thai businessman, with shipments arriving in the beginning of 1969.