What does the science show about lepomis crosses. There is quite a bit out there and some of it is surprising. That said lets start with the seminal paper by Childers. I picked out a few points to ponder. Note the difference in the % male offspring in reciprocal Rm X Gf (70%)and Gm X Rf (50%). That last # means the primary reason (other than catchability) being low reproduction is missing from half (low viability half - G X R) of the R X G pairing and still much higher than HBG ( 90%+) in the other pairing . Lots of babies means high potential stunting. Where was this thread going ? \:\)

HYBRIDIZATION OF FISHES IN NORTH AMERICA
(FAMILY CENTRARCHIDAE)
by

W.F. CHILDERS
Illinois Natural History Survey
Urbana, Illinois
U.S.A.

In this paper R refers to red-ear sunfish, B to bluegill, G to green sunfish, and W to warmouth.

4.1 Sex Ratios of F1 hybrids
Sexually mature F1 hybrids were collected from each population and sexed. Of the 10 kinds of viable F1 hybrids, seven were predominately males (RB, BR, and BG were 97 percent males; WG were 84 percent males; and RG, GB, and BW were approximately 70 percent males), two were approximately 50 percent males (GR and RW), and one was predominately female (GW was 16 percent males). Ricker (1948) determined the sex of 428 BR F1 hybrids in Indiana and found them to be 97.7 percent males.


The R × G, G × B, and W × G pairing successfully hybridized each time they were tested.

4.2 Reproductive success of hybrids
The reproductive success of each of the 10 kinds of viable F1 hybrids was investigated in one or more ponds. The occurrence and abundance of F2 hybrids were determined by seining, trapping, shocking, poisoning or draining the ponds after the F1 hybrids were one or more years of age. RB, BR, and BG failed to produce abundant F2 generations when in ponds which contained no other species of fishes. In contrast to these results, BR F1 hybrids produced abundant F2 generations in two ponds in Indiana (Ricker 1948). The other seven kinds of F1 hybrids produced abundant F2 populations when stocked in ponds containing no other fishes. Three of the seven kinds of F1 hybrids which produced large F2 populations when stocked in ponds containing no other fishes were also stocked in ponds with largemouth bass. RG F1 hybrids and GB F1 hybrids, when stocked with largemouth bass, produced only a few F2 hybrids. No F2 hybrids were found in the pond stocked with BW F1 hybrids and largemouth bass. WG F2 hybrids and GW F2 hybrids were stocked in ponds containing no other fishes. Both of these F2 hybrids produced large F3 populations.


4.4 Rate of growth
In an attempt to determine whether certain F1 hybrid sunfishes actually grow faster than their parent species, two experiments were conducted in which equal numbers of uniformly sized F1 hybrids and parent species were stocked in ponds which contained no other fishes. Intraspecific competition is keener than interspecific competition because individuals of the same species are more nearly equal in their structural, functional, and behavioural adaptations. Consequently in experiments designed to compare rates of growth, it is imperative to use equal numbers of similarly sized fishes. In the first experiment the growth rate of BG F1 hybrids was compared to that of green sunfish. In the second experiment the growth rates of GR F1 hybrids, green sunfish, and red-ear sunfish were compared.

In both experiments the average increase in total length of the hybrids was not significantly different from the increases of the parental species. The population densities of the fishes in both ponds were much lower than would be found in most normal natural populations. In both experiments intraspecific and interspecific competition was undoubtedly quite light; consequently, the question of whether certain F1 hybrid sunfishes are superior to their parent species in rate of growth cannot be answered until high density populations containing equal numbers of equal sized hybrids and parent species are studied.