http://forum.aqua-fish.net/ A forum devoted to aquarium fish, plants, techniques and fish keeping as a whole. en http://forum.aqua-fish.net/?topic=how-do-you-tell-the-sex-of-an-oscar#1 need to know vanessa 2008-07-19 http://forum.aqua-fish.net/?topic=how-do-you-tell-the-sex-of-an-oscar#2 Sexing Oscars if quite difficult. You need to look underneath each fish in order to determine if it’s male of female. The sex organ is placed near the fish’s anus. Females have small hole there. http://www.aqua-fish.net/show.php?h=oscar jan 2008-07-20 http://forum.aqua-fish.net/?topic=how-do-you-tell-the-sex-of-an-oscar#3 I have heard that experienced oscar keepers can know at a glance the sex of the fish.The only other way that I know different to what Jan has posted is that if you have the two fish of exactly the same age the male will be more colourful and larger. But the problem is knowing if the fish are the same age mickey 2008-07-21