How to Sex an Oscar Fish - Male or Female?
How can I tell the difference between a male and a female Oscar? If I had a pound for every time I got asked, or came across this question, I would be quite a wealthy person. Okay, let's get one thing straight. You cannot tell the difference between a male and a female Oscar just by looking at them in the tank. I have read many posts on different forums which claim that it can be done by comparing fins and colouration. These people are wrong so please ignore those posts, they are completely erroneous. Oscars are what we call monomorphic, this means that male and female look the same. YOU CANNOT TELL THE SEX JUST BY LOOKING AT THEM.
So, if you can't tell the sex of an Oscar just by looking at them, how can it be done. Most people finally find out the sex of their Oscars by observing them when the female start laying eggs. If you have got a pair that are the same age then the chances are, they will become sexually mature at around the same time. Once you have seen a female Oscar laying eggs, it is very easy to recognize. It is oval in shape, rather blunt and whitish Iin colour, a little bit like the end of an egg. If the other Oscar is a male and he is sexually mature, his sexual organ will protrude from underneath him. The easiest way to describe his "member" is it looks rather like a little spike or thorn. There is a distinctive difference between male and female sexual organs, you cannot confuse them.
One thing to remember, female Oscars will lay eggs whether there is a male presence or not. If you have two females, the chances are you will see one laying eggs and the other one may, or not show an interest, but probably won't have any sexual organs visible. If you have two males, the chances are you will never see their sexual organs.
Oscars and many other fish in general will come into spawn once a month. If you want to encourage your Oscars to spawn, then keep your water on the warmer side, around 28°C. Keep the water in very good condition with regular water changes. This will give you the best chance of successful breeding. Don't be too disappointed if they don't spawn every month, because they are captive bred Oscars, there is a strong possibility that they won't act quite the same as if they were in their natural environment.
If you are desperate for a breeding pair, ask at your fish shop, some breeders may be able to supply you with a male and a female. Don't take this the Gospel, you will have to ask.
One final note, please don't undertake any kind of breeding programme without researching first.