Topwater -- I suspect that Greg and Shan are thinking of some of the old work at the Illinois Natural History Survey. A guy by the name of Dr. William Childers did a lot of experimentation with sunfish crosses. I've got a copy of his report from 1967, and it has very nice color plates of the various crosses among bluegill, redear sunfish, green sunfish, and warmouth (incidentally, the warmouth were apparently pretty far removed from a genetic perspective and did not cross as well as the others).
Anyway, Dr. Childers used both male BLG and female RES to get the cross, and also made the opposite cross (male RES X female BLG). In both cases, the offspring were 97% male, which is one of the earlier citations I know of the tendency for the hybrids to be primarily one sex.
He also said that when the first generation hybrids (F1) were stocked in a pond with largemouth bass, they produced very little of an F2 generation. However, when the F1 hybrids were put in ponds by themselves, the F2 generations were abundant. So, even with 97% males, there still was fertility.
A little history lesson!! :-)
Dave
