were proof that direct genetic isolation did not exist 
between the bluegill, green sunfish, and red-ear sun- 
fish. Incubation times of fertilized eggs from all Py 
crosses were similar when incubation temperatures 
were similar. Eggs incubated at 70 degrees F. began 
hatching 47 hours after fertilization, and none hatched 
later than 61 hours after fertilization. The larvae be- 
one of these ponds became contaminated with female 
bluegills and the other two ponds dried up during the 
summer. The BxR cross has been made experimentally 
with success six times in Indiana (Krumholz 1950). 
The R x B cross was tried in four ponds. In three 
of the four ponds, no hybrids were produced. In the 
fourth, 11 young sunfish were found when the pond was 
Table 2. — Field crosses attempted by placing adult males of one species and females of another species in ponds con- 
taining no other fish. Ponds were stocked in May or early June and were censused by being drained, seined, or chemically 
treated the following August or September. The species used were bluegill (B), green sunfish (G), and red-ear sunfish (R). 
Py Cross Size of Pond 
(Male x Female) (Surface Acres) 
RexaiG 
RxG 
*Size of pond estimated, 
The 11 young sunfish found were too smal] to be identified as hybrids or as young of parent species. 
came free-swimming fry during the fifth or sixth day 
after hatching. 
One group of green sunfish eggs fertilized with blue- 
gill sperm was accidentally incubated at temperatures 
ranging from 70 to 95 degrees F. Many of the BG Fy 
hybrids produced from this group of eggs had very short 
caudal peduncles. In a few of these fish, the posterior 
end of the caudal fin did not extend beyond the poste- 
rior edges of the soft dorsal and soft anal fins. 
Field Crosses. — Hybrids were produced in 4 and 
possibly 5 of the 16 ponds used in the experiment re- 
ported here, table 2. 
The R x G cross and the G x B cross, each cross 
tried in two ponds, resulted in the production of large 
numbers of Fy hybrids. 
The B x R cross was attempted without success in 
three ponds. These were all improper tests because 
Number of 
Adults Used 
F, Hybrid Remarks 
Generation 
Yes Hybrids abundant 
Yes Hybrids abundant 
8 No — 
No -——— 
No 
Hybrids abundant 
Hybrids abundant 
Contaminated 
Contaminated 
Contaminated 
Pond went dry 
Pond went dry 
11 young foundT 
drained. These young sunfish were so small (0.25-0.50 
inch total length) that it was impossible to identify 
them as hybrids. An attempt to raise them in the lab- 
oratory failed. However, circumstantial evidence in- 
dicates that they were RB Fy hybrids. When the pond 
was drained, the parent fish were sexed by dissection 
and only male red-ears and female bluegills were found. 
If this pond had been contaminated with male bluegills 
or female red-ears, it is probable that several thousand 
young would have been produced. 
The B x G cross was attempted in two ponds. Both 
ponds became contaminated with male green sunfish, 
and in each pond large numbers of young greens were 
produced. Consequently, these ponds gave no real tests 
of hybridization between bluegill males and green fe- 
males. 
The G x R cross was set up in three ponds. No 
