Oscars are what we call monomorphic, meaning that male and female look the same. This means that you can't go to a shop and choose a male and a female like you can with other species of fish. Contrary to a few people's belief, you cannot tell the sex of an Oscar by the shape of its fins, the length of its body, or even it is colouring. You will normally only know the sex of your Oscars when they start laying eggs.
Cichlids can be very picky and females won't necessarily breed with the first male that swims their way. To begin with you have to obtain a male and female, you may get lucky if you buy two Oscars, however normally the easiest way to obtain a male and female is to buy several Oscars and wait for them to pair off. However, this can take many months, even years before it happens. Even if your fish to start laying eggs, there is a very high chance that the eggs will not be fertile. Some fish are born infertile because of the way the fish breeder has spread his fish and what chemicals he they have used. I'm afraid that there is no easy way to successfully breed Oscars in captivity, it really is down to luck at the end of the day.
I don't think you can actually determine when an Oscar will become sexually mature by its size alone. Depending on what you feed your fish, what size tank you keep it in, and how well you look after it will play quite an important role in the growth of the fish. The Oscars that I keep in my 300 gallon tank are considerably bigger than the ones in the 125 gallon tank. They actually started laying eggs in the different tanks at virtually the same time, at around 18 months old. For this reason, I'm quite confident in my belief that Oscars are not quite ready to breed at one-year-old. Having said that, this is just my experience with three lots of Oscars. it is also worth noting that Oscars will not pair off until they become sexually mature so you will have a long wait if you buy them as babies.Only when Oscars start laying eggs will you know for sure that you have got a male and a female. The females egg tube is overall in the shape, not unlike the pointed end of an egg. The males sexual organ is pointed and looks rather like a thorn.
Female Oscars Egg Tube
Oscars prefer to lay their eggs on a flat surface, they will not lay their eggs directly on the substrate. If there is nothing in the tank for them to lay their eggs on, they will clear a patch of gravel/sand until the bottom of the tank is exposed and then they will lay their eggs there. If you want your Oscars to breed then you are probably wise to put something in the tank like a piece of flat slate or rock. They like to clean the surface of the rock vigorously before they lay their eggs. It's amazing how clean they will get the rock, there will be absolutely no sand or gravel left on it whilst they are going through this process of cleaning the rock.
Oscars will often choose a location for where they are going to start laying eggs a long time before they actually start breeding properly. I also believe that Oscars go through a kind of dress rehearsal before they actually start laying eggs. The reason I say this as I have observed my Oscars going through a similar procedure in exactly the same way they would if they were actually laying eggs. Fish will survey an area before deciding whether or not it is suitable. After all, breeding is probably the most important thing that goes on in nature and animals will go to great extents to make sure their offspring survive.
Oscars will often choose a location for where they are going to start laying eggs a long time before they actually start breeding properly. I also believe that Oscars go through a kind of dress rehearsal before they actually start laying eggs. The reason I say this as I have observed my Oscars going through a similar procedure in exactly the same way they would if they were actually laying eggs. Fish will survey an area before deciding whether or not it is suitable. After all, breeding is probably the most important thing that goes on in nature and animals will go to great extents to make sure their offspring survive.
A pair of breeding Oscars will go through various rituals such as lip locking, also known as jaw locking, you may also notice them chasing each other around the tank, nipping at each other and performing what sometimes looks like a very rough behaviour. Your Oscars may perform all of these strange behaviours, or just a couple. It is quite rare, but sometimes they don't do any of them. if you do start seeing your Oscars performing these strange behaviours, don't get too excited, it can often be many months before they actually start laying eggs. A short time before they start laying eggs, one or maybe even two days, they will go off their food. You will have probably observed them acting strangely such as excavating the substrate, as in picking up mouthfuls of gravel/sand and moving it to another part of the tank.
If your Oscars have located somewhere to lay eggs, such as a flat rock then they will become extremely protective towards this area and no other fish will be allowed anywhere near it. Oscars like to give the rock a thorough clean using their lower jaw. The strange protrusion that many Oscars develop on their lower jaw is in almost the exact spot that they use to clean the rock. It certainly makes you think that this may have something to do with this type of behaviour. At feeding time, your Oscars may still come up for food but you may notice them swimming straight back to their rock after maybe only eating a small amount of food. You must be aware that Oscars are fairly strong fish and are more than capable of moving large flocks around the tank. I would strongly advise you not to put the rock there any breakable objects such as heaters. The Oscar shouldn't have the strength to break the aquarium glass, if it has, you are using the wrong type of tank. A day or two before the Oscars lay eggs, they will probably go off their food. As in nature, the fish will also stop eating when they spawn. Oscars more than often lay their eggs in the evening, or at night. So in many circumstances, many people wake up to a very nice surprise.
When the Oscars are ready to lay eggs, you will see their sexual organs protrude from underneath them. The female Oscar will then start swimming over the area where she is going to lay. She could well spend quite a long time moving around in circles, rubbing her underside on the surface of where she is deposit the eggs. All of a sudden you will start to see tiny white eggs appear. They will be perfectly round little white eggs but she won't lay the eggs all in one go. She may lay a few eggs and then let the male swim over the top and fertilise them. When all of the eggs have been laid, both the female and the male will hover over the eggs and fan them with his pectoral fins. This is to oxygenate them. They will also become very protective and aggressive. Any fish that dares to go near the eggs can expect a very hostel reception and more than likely will receive a good hiding. Also, don't be surprised if you see the Oscars eating the odd egg, they are not just feasting because they are hungry, they will eat any unfertilized or bad eggs, this is quite normal.
If after a few hours you start noticing a cotton wool type fungus growing on the eggs, there is a very good chance that all, or some of the eggs are infertile. Unfortunately, the fungus may start attacking good eggs as well. There's not a lot you can do about this. This is one of the reasons why methylene blue is used, it can help to prevent and treat fungus on eggs. A word of warning! Adding methylene blue to your main tank could destroy your biological filter. In other words, you will lose all your beneficial bacteria.
If after a few hours you start noticing a cotton wool type fungus growing on the eggs, there is a very good chance that all, or some of the eggs are infertile. Unfortunately, the fungus may start attacking good eggs as well. There's not a lot you can do about this. This is one of the reasons why methylene blue is used, it can help to prevent and treat fungus on eggs. A word of warning! Adding methylene blue to your main tank could destroy your biological filter. In other words, you will lose all your beneficial bacteria.
The eggs normally take 3 days to hatch. If they are fertilised they should turn a lightish tan colour. If they stay white, they are not fertilised. You may notice the Oscars appear to eat the odd egg, this is exactly what they are doing. They know a bad egg and will remove it straightaway. Don't be surprised if you wake up in the morning and all the eggs have gone. This is very common and happens more often than not. Various things contribute to this happening such as eggs that are not fertilised or parents that have been spooked in some way. It is very common for fungus to grow on the eggs, this normally happens to unfertilized eggs. If you have a mixture of unfertilized and fertilized eggs then the Oscars should remove them. If there are lots of dead eggs amongst fertilized eggs than the fungus may attack the good eggs.
Fertilised Oscar Fish Eggs
This Oscar fry is 2 hours old
When the eggs to hatch, the fry will be totally helpless, they will appear as a wriggling mass attached to the rock., at this stage, they don't need food. The Fry will have a yolk sac that will feed them for around four days. Once the yolk sac is gone, the Fry will then need feeding. They need feeding a lot and they need to be fed the correct food. If you do neither of these, they will die very quickly. Before we carry on, we better address two points. Are you absolutely determined that you want a brood of baby Oscars that survive or are you not really bothered? If you would like to see the Oscars look after their young then you will have to accept the fact that the Oscars may eat the eggs or the Fry. If you want to take it very seriously and you definitely want lots of baby Oscars then you will really need to remove the eggs from the tank before they hatch. Don't worry, you can artificially hatch the eggs, they will hatch without the parents being present.
This is what you need to do. If the eggs have been laid on something that can be removed, like a piece of rock then take it out and place it in a small container that is big enough to cover the eggs to a depth of around 6 inches. You can be absolutely sure that the Oscars will not be happy about you taking their eggs so expect them to attack your hand. You should fill this with water from the main tank making sure that it is in very good condition. You need to have around 5 inches of space all around the rock. If the eggs are on a thin rock then you need to prop the rock up so it is at an angle. You want the higher end to be around two or 3 inches. You then need to place an air stone under the higher end and try and set it so the bubbles are released around the eggs. You don't want to have the bubbles shooting so fast that they disturb the eggs though.
This is what you need to do. If the eggs have been laid on something that can be removed, like a piece of rock then take it out and place it in a small container that is big enough to cover the eggs to a depth of around 6 inches. You can be absolutely sure that the Oscars will not be happy about you taking their eggs so expect them to attack your hand. You should fill this with water from the main tank making sure that it is in very good condition. You need to have around 5 inches of space all around the rock. If the eggs are on a thin rock then you need to prop the rock up so it is at an angle. You want the higher end to be around two or 3 inches. You then need to place an air stone under the higher end and try and set it so the bubbles are released around the eggs. You don't want to have the bubbles shooting so fast that they disturb the eggs though.
You should then add some methylene blue to the water until it turns dark blue. This is used to help prevent and treat fungus on eggs. Keep the temperature at a constant level until the eggs hatch. After a while, the fry will fall of the rock, when they have all fallen off, remove the slate. Once the yoke sack has disappeared, you can start feeding them. You can now transfer the fry into their own tank now. This is now the crucial part of breeding Oscars. The tank doesn't have to be very big, 10 or 15 gallons will suffice. If you put them in a tank that is too large, they will not be able to find their food easily enough.
Baby Oscar Fish
There is quite a high mortality rate in fry so don't be surprised if quite a few of them die. You cannot feed them on normal fish food, you have to give them something that is small enough and full of nutrition. Baby brine shrimp is a very common food source for young fry. Brine shrimp can be hatched out at home which will save you time and money going back and forth to the shops. Some people have success in raising fry on the special ood that is made for fry, these type of food contain tiny particles that are small enough for them to eat. If you don't want to go down the route of using brine shrimp, then ask your fish store if they can provide you with special food for fry. It won't take that long before you can start introducing various other types of food, maybe blood worm, small krill, also flake food can be fed to very small Oscar's at the beginning and then slowly move them onto other foods such as very small pellets.
Eggs Aren't Hatching
It isn't uncommon for a male and a female to lay eggs, go through the whole procedure of fertilising them only for the eggs not to hatch. In cases like this there is a strong possibility that your fish are sterile. Breeders often use various chemicals to prevent fungus growing on the eggs. Some of these chemicals can affect the fry and render them sterile from birth. It doesn't affect their health, it just means that they won't be able to reproduce. One of these chemicals that is known to affect eggs is called "Acriflavin". Since a lot of fish are bred abroad, it would be virtually impossible to find out what chemicals have been used in the breeding process.
Female Oscars are very good mummys. Even if the eggs are not fertilized, they will often look after and protect the eggs for quite a few days. They then may just get fed up and leave the eggs where they are, however they often eat the remaining eggs.
Fry May Not Survive
Don't be at all surprised if your fry perish in the first few days. There is a very high mortality rate with young hatchlings. In the wild, around 90% of young baby Oscars will die in the first couple of months. You should fare slightly better when breeding in captivity
Finally
Female oscar fish will not necessarily breed with the first male that happens to swim by. In fact, many fish are very particular who they breed with. Even though you may have a male and female it doesn't necessarily mean they will automatically pair up and start breeding. Females will only breed with males that they like and think will carry on their genes. If a female isn't happy with the male even though it may be the only one in the tank with her, they may never breed.
(Article Source : http://www.oscarfishlover.com)
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