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If you are serious about breeding Oscars, you must have at least two large fish tanks than can handle multiple fish. One of these should be at least 200 gallons while the other should be 70 gallons or larger. Oscars are large fish often reaching a foot long in the aquarium environment. Some can get close to 18 inches long in a large, well-filtered tank.
The 200-gallon tank should have enough filtration to change out the water once every thirty minutes, so a filtration system that can handle 400 gallons an hour or more is the best bet. You will also have to have a heater system in place that can keep the water temperature between 78F - 84F.
Oscars are apt to move things around in your tank. Minimal decorations are advised (unless you like replanting stuff every day). These decorations should be heavy enough that the fish can't move them. A couple of large rocks buried deep in the substrate work well. You could anchor a few fake plants underneath these rocks to keep them from being pulled out as well. You also need a flat stone of some sort for the female to lay her eggs on. A piece of slate works nicely for this.
Unlike many of its Cichlid cousins, the Oscar does not need a pH around 8.0 to survive and breed. They do well anywhere from a pH of 6.5 to 8.2. The only requirement is that this level stays consistent throughout the life of the fish. If a huge change in pH doesn't kill the fish, it could still do damage to its reproductive system as well as promote Oscar fish diseases.
An unhealthy fish or an unhealthy environment will mean no breeding. It is important to monitor the chemical levels in your tank, and do 25% water changes on a weekly basis to keep the nitrogen levels down.
Selecting Mates For Successfully Breeding Oscars
Oscars are one of the few freshwater aquarium breeds that chooses a mate for life. This is important to understand because the female Oscar will not just take to whatever male is hanging around. She will be quite particular about her mate. It's also helpful to know that there is no way to physically sex the fish until they are breeding. If you are looking to breed Oscars, you will either need to purchase a proven breeding Oscar pair or get several young Oscars and raise them in the same tank.
If you purchase a pair of breeding Oscars, there is no guarantee that they will breed in your tank. Sometimes when they are moved from one environment to another, they simply stop reproducing and there is no proven way to get them to start up again.
On the other hand, you can buy several young Oscars, put them in a tank, and wait for a set to pair off. This process can take up to two years (if it happens at all), so you'll want to have a large tank that can handle six or more foot long fish. It is suggested that you use at least a 90-gallon tank, although a 200-gallon or 300-gallon tank is much more suitable for a breeding pair.
If you purchase less than six Oscars, the strongest few will kill off the weaker ones and cause a very stressful environment in the tank. In a stressed environment, it is very unlikely that any fish will pair off.
The easiest way to identify when two Oscars pair off, is to look for a Jaw locking behavior. This looks very similar to fish French kissing. The pair will also chase each other around the tank and possibly run into each other roughly. Once this happens these fish will claim a territory in the tank and attack any other fish that try to enter it.
At this time, you should remove any other Oscars from the tank to prevent fighting that could leave the paired off fish injured or dead.Don't move the breeding Oscars, as a new environment could cause them to split up, and you'll lose all the time you've spent getting them to mate.
Mating Rituals Of Breeding Oscars
Once a set of Oscars has paired off, the mating rituals will begin. This ritual can last for months before any actual spawning occurs. Your Oscars will lock jaws, chase each other around the tank and engage in rough play. In the days before the first spawning attempt your fish will stop eating. Don't worry this is a normal part of Cichlid behavior.
They will redecorate the tank at this time too, picking up substrate in their mouths and redistributing it into mounds. You will notice both the male and female starting to clean off a flat surface in the tank. This is why the flat rock should have been installed. They will clean it until there is absolutely nothing on it. They won't leave the general area of this nest until the fry have all hatched several days later.
Just before the female begins to lay her eggs, you'll see her sexual organ protrude (this is the only time you'll be able to sex your fish). She may spend hours circling the clean, flat surface before beginning to lay her eggs. She won't lay them all at once.
Once she has laid her first set of eggs the male will swim over the top of them and fertilize. This process will continue until the female has no more eggs to lay. In the end there could be as many as 1000 eggs.
The Unique Parenting Style Of Oscars
While Oscar fish won't win any parenting awards, they do more than some spawning fish. Once the eggs are laid, the parents will begin to root out all the unfertilized eggs (these will be white) by taking them into their mouths and either eating them (which happens most of the time), or by spitting them out into the substrate.
Fertilized eggs will be slightly translucent and more tan in color. Sometimes a fungus will attack the eggs. This will look like white cotton candy or cotton strands. The Oscars will attempt to remove any eggs with fungus on them. If the fungus cannot be eradicated, the Oscars will eat the entire brood.
Breeding Oscars Successfully
A successfully fertilized egg will hatch in 36 hours. If your eggs haven't hatched within this time and are still around, they will become fish food. It is very common for the first few spawnings to fail.
If your Oscars fail to conceive after four or more attempts, you may have encountered an infertile male or female. This is likely due to the use of the chemical Acriflavin. Acriflavin has been proven to affect he reproductive health of many Cichlids. Because many of the Oscar breeders are located overseas, it is all but impossible to find out if your Oscar was treated with this chemical prior to being sold.
If the Oscars are successful in breeding, then you may find yourself with up to 1000 fry to deal with. For the first three or four days the fry will live off their egg sacs. They won't move off from the flat surface where they were laid, instead they'll just wiggle around there rather helplessly. At this point, he male and female Oscars will still continue to protect the brood. When the fry shed their egg sacs though, all bets are off and the fry are as likely to become food to their parents, just like any other fish in the tank.
In the wild, the mortality rate of Oscar fry is estimated to be around 90%. In your tank environment, the mortality rate can be cut to under 5%. If you want your fry to live you should remove them to a new tank. This could be the smallest of the two original tanks, if they aren't still housing your non paired Oscars. Once they are relocated, you can feed them either powdered fish food or brine shrimp. Although both are satisfactory foods, brine shrimp will help the fry grow faster.
If you are brave enough, you can remove the eggs from the tank before they hatch. Mind that the parents will not be happy with this and will attack you. If you are going to remove the eggs, take the entire rock that they are laying on out of the tank instead of trying to scoop them up. Wear thick gloves, Oscars don't nip they bite.
If you have successfully bred Oscars, you may be able to find a pet store willing to buy them from you. After all, what are you going to do with 1000 Oscars? Successfully breeding Oscars could become a full-time job if enough merchants around your area are interested in your stock.
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