This is a population genetics problem. Don't think of it as adding bass think of it as adding genes to your bass population. This relationship is explained by the Hardy-Weinberg equation "F^2 + 2FN + N^2" F= the frequency of genotypes that are Florida strain N= the frequency of genotypes that are northern strain. FN= the ones that are mixed genotypes.If you had 100 pure F1s they all have half and half, all FN. The frequency of F is .5 x 100 and N is the same. And it would stay that way with out selective pressure. If you harvest only the largest fish, or if florida strain are more likely to die under ice eventualy the frequency of F goes down. Fewer and Fewer of the fish are F1s, becasue thier are fewer florida genes in the pool. Now you have 100 fish, but only a fourth of the genes are florida (the other half of the genes died) then the ratio is 6.25 pure florida strain, 37.5 F1s, and 56.25 pure northern strain. You don't have to kill off the Florida strain to get the same results, any change in genotype frequency gets similar results, and genotype frequencys are always changing because some fish are always better suited to a particular enviroment. Add the F1s, then keep all the fish that are too skiny (or whatever criteria your shooting for), eventualy the fish will evolve into the type you really want.