This is a pretty rare tilapia. Very aggressive and quite dark in color. I have to remove the top lip of the males to keep them from killing the females. The females are slow to mature and breed in my experience, but the males will breed at just 4 months.

This tilapia is unusual in that rather than using the XX/XY system for sex determination, like we do, it uses a ZZ/ZW chromosome system with the males being ZZ and the females being ZW. The O. mossambica uses the XX/XY system with females being XX. A cross between the ZZ male and the XX female produces offspring that are all ZX and this turns out to be male hybrid fish. Being hybrids they also grow very quickly.

Mike Sipe has been breeding these for body shape for over 30 years. The hybrids retain the male body shape and fast growth. His tests say the hybrids can reach one kilo in under 9 months.

This picture shows a larger improved hornorum in contrast with a batch of unimproved fish:
http://s25.photobucket.com/albums/c70/b ... proved.jpg

Male breeders are quite expensive at around $150 each, but it gives you the ability to produce thousands of fry a months that are nearly all male and not use hormones for sex reversal.