Size doesn't always determine the sex right away. The sex isn't established until they pair off at which point one under goes a sex change. When this change occurs, the female becomes bigger to make room for offspring.
It could be that the 2 have not paired yet. The size difference could simply be that one is older then the other. It is very likely that the bigger one will become the female. Its important to remember that though 4inch is big for an aquarium in the ocean what would be considered normal.
I have always been amazed at the size of fish seen in the sea compared to the "babies" we keep in our aquariums.
Last edited by Renegade; 03-31-2011 at 09:55 PM.
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