Breeding Oscars
Breeding Oscars is pretty much a matter of leaving them alone and letting them do their thing. The most trying task for the aquarist is finding a mating pair, which is a gamble in any case. If your Oscar is adult in size, and you want him or her to breed, it becomes a very trial-and-error process to find a mate. You need to know whether you have a male or female, and that is a difficult determination in itself; you need to be able to sex the intended partner correctly. Then, even if by the Grace of God you do have opposite sexes, THEY have to want to mate.
Probably the most common and effective method of putting together a mating pair of Oscars is to buy 6 or 8 young specimens (about 1 inch in length), and allowing them to grow up together. The likelihood that you have both males and females is good, and the chances of a mating pair forming is also good. You need to have a plan for the "extra" fish after your pair forms -- selling them back to the LFS, giving them to friends, moving them to other aquariums -- because, as you know, 8 Oscars would need an aquarium the size of your garage after they become adults.
A mating pair becomes evident because of mating "play", which is a seemingly aggressive behavior towards each other; lip-locking, tail-slapping, quivering. One odd thing is that they will open their mouths in huge "yawns" in unison. If one of the fish is overly aggressive, and the aggression is obviously one-sided, then separate them. Although this mating play is rough, it does not involve one fish dominating the other.
According to Dr. Axelrod, the ideal mating temperature is 78 degrees; other sources claim 83. The important thing is to keep the temperature, whatever it is, constant. Your tank preparations should include 3 important things: Temperature, placing a flat rock on the floor of the aquarium, and planning what to do with the fry. During their play, the Oscars, using their mouths, will clear the gravel off of the flat rock, and then the female will lay her eggs. The eggs are laid in neat, linear rows in a circular pattern on the flat surface. No egg will be laid on top of a previously laid egg. Not all the eggs are laid at once; the female will take breathers, at which time the male moves in and fertilizes the eggs.
After the eggs are laid, both parents-to-be will hover over them, fanning the eggs with their fins. Fanning keeps water moving over the eggs, keeping them oxygenated and keeping sediment from settling on them. Occasionally they mouth the eggs, which keeps them clean and turns up bad eggs, which are then destroyed.
If a constant tank temperature is maintained, the eggs should hatch in about 36 hours. At first, the fry cannot swim, but they squirm "en masse" on the rock, living off the egg sac, for about 4 days. The parents constantly attend to their young at this time. After the sac is used up, the fry become "free-darting" (I hesitate to call it "swimming" yet).
Feeding these fry is easier than other breeds, because of the baby Oscar's relatively large size. A good and simple plan is to crush regular processed flake food in your fingers, and just drop it in. Turn off filtration during fry feeding time to make it easier for them to find their bits of food.
The size of an Oscar spawn can be anywhere from 300 to over 1000 fry. In the wild, only 10% of a spawn can expect to live past one inch in length.
How the parents act towards their fry is as individual as each Oscar's personality. Some have spawn after spawn and never bother their fry; others eat their young as soon as they hit "darting" stage. Many will eat their fry the first couple of spawns, then learn to leave subsequent spawns alone. To be on the safe side, separating the fry from their parents is probably a good idea. Oscars can be very good parents; any other fish that dares to threaten an Oscar spawn can expect a good thrashing!