Steve_, the high proportion of males has a lot to do with lower reproduction. As to fertility and viability the literature isn't always in agreement. Fertility is the ability of crosses to produce gametes and engage in reproductive activities. Viability deals with whether those gametes can form viable unions that result in hatch fry that can grow up. As far as I know, all lepomis first generation crosses highly proportioned to be fertile and viable. They sometimes do not succeed in attracting mates with parental species. Some work and some researchers challenge even hybrid vigor ... but to be sure there is out depression and the offspring of lepomis Fx can be an odd lot.

I have read that although the F1 generation can generally cross and backcross ... subsequent Fx have much lower fertility and viability rates which greatly affects reproduction. This is true of F1 backcrosses and F1 crosses with F1s. There is at least one F1 cross that produces completely infertile polyploid offspring (BG x PKS). It is thought that lower fertility and viability of Fx offspring provides barriers to genetic infusion between species of lepomis. In other words, it is widely thought that hybridization doesn't lead to new species or help to bring new genes into a species from another. Environment and genetic mutation are thought to contribute most to speciation.