As with most members of the animal kingdom that lack obvious genitalia, discerning the sex of an Oscar Fish can be almost impossible. They are monomorphic, meaning male and female look exactly the same in size, shape and color. However, there is a way to determine the sex an Oscar Fish.
- Observe possible reproduction
The easiest way to sex an Oscar Fish is to watch for any sign of reproduction. A female will swim along the bottom of an aquarium and deposit eggs. A male will follow close behind and fertilize with semen.
- Examine reproductive organs (venting)
Although Oscar Fish male and female have quite different reproductive organs, they are small enough that it can be hard to differentiate. An egg tube on a female will protrude from the same area as her anus. The male sexual organ looks like a small spike.
- Ask for a professional opinion
If you cannot discern if your Oscar fish is male or female, ask for a professional examination by a breeder or local expert.