No, my understanding is that the hybrids in general are not sterile. It is just that the most commonly sold hybrid is a GSF female X BG male and that particular cross is usually in the high 90% range of males. Both the males and female hybrids are fertile, but there are just few females produced therefore few potential eggs produced.
I have read a research paper where when some unusual hybrid crosses were done in the lab that normally do not happen in natural environment, the researchers came up with some unusual fish behavior that prevented the F1's to be able to successfully raise young. In one case as I recall, the males made nests but were so aggressive at protecting the nests and fighting amongst themselves, they continually scared the females away and were never able to get natural reproduction. But these were in odd crosses that normally do not happen naturally.
The GSF female X RES male is supposed to be an easy cross to occur naturally, likely more so if mates of their own species are not readily available to mate with. In other words where the researchers put only male RES and female GSF in the pond and there were no other options for spawning, the hybrids were readily created without fail.
Last edited by snrub; 07/28/15 03:24 PM.
