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HYBRIDIZATION OF FISHES IN NORTH AMERICA
(FAMILY CENTRARCHIDAE)
by

W.F. CHILDERS


R � RW, W � RW, B � RW, G � RW, R � GB, and RB � W young were killed after they developed into free-swimming fry because of the lack of ponds in which they could be stocked. All six kinds of fry appeared to be normal and probably would have developed into adults. Free-swimming fry of the remaining six crosses in the laboratory were stocked in ponds and did develop into adult fishes. BW � B, G � GW, and B � RG populations produced large numbers of young.



Both WR and WB F1 hybrids exhibited high mortality between the hatching and swim-up fry stages. At the time the experiments were terminated, only two percent of the WR hybrids and one percent of the WB hybrids appeared to be morphologically normal. All of these morphologically normal-appearing WR and WB F1 hybrid fry were very sluggish. When petri dishes containing these hybrid fry were tapped with a pencil, the fry responded with weak swimming movements or not at all, and it is very doubtful that any of these fry would have become free swimming. Fifty-five percent of the WG hybrids and 75 percent of the pure green sunfish zygotes developed into normal-appearing swim-up fry (difference significant to 0.05 level). The WG hybrid swim-up fry appeared to be behaving normally. The remaining nine kinds of hybrids were not significantly different from their maternal parent species in the percentages that developed into normal swim-up fry.

Table III

Successful backcrosses, outcrosses, four-way cross, and another cross involving F1 hybrid sunfishes.1

Backcross -Outcrosses -Three-Species Cross -Four-Species cross
♂ � ♀

R � RW ---R � GB ------RB � GW ----------------BW � GW
G � GW ---R � BW
W � RW ---R � GW
BW � B ---B � RG
-----------R � RW
-----------G � RW
-----------RW � W


1 R = red-ear sunfish, B = bluegill, G = green sunfish, W = warmouth.