My pollenii are proving pretty easy to sex. The males are darker with more bulbous foreheads and longer fins. Like another poster said....the older they get the more noticeable the characteristics become.............larger body, longer more pointed fins, more pronounced foreheads-not like a Frontosa-just more contured than the female. I have had 10 fish growing up together in a 65 gal tank for a few months, and have been moving male/female pairs to separate tanks. In the original tank there has constantly been an Alpha male ready to replace the removed one.