HYBRIDIZATION BETWEEN 
THREE SPECIES OF SUNFISH (Lepomis) 
American agriculturists have produced many hybrids 
for increasing food production or for improving the qual- 
ity of food products. Corn and poultry hybrids are so 
commonplace that they are considered normal crops 
for progressive farmers. The use of other types of plant 
and animal hybrids on the farm is spreading, and it 
would be no great step for farmers to accept the idea 
of hybrid sunfish in their pasture ponds. 
The need for a hybrid fish in pond culture relates 
largely to the problem of population control: many kinds 
of warm-water fishes reproduce so successfully that 
they create conditions of overpopulation and become 
severely stunted. Stunted populations of fishes are use- 
less for recreation or food. A hybrid fish with a reduced 
reproductive potential would be a great improvement 
over the fishes now commonly used in warm-water ponds, 
particularly if it combined rapid growth to a large size 
with other characteristics desirable for angling. 
Naturally produced hybrids of fresh-water fishes 
are not uncommon and have been reported in the salmon 
family (Salmonidae), sucker family (Catostomidae), 
minnow family (Cyprinidae), pike family (Esocidae), 
sunfish family (Centrarchidae), and some others. Moenk- 
haus (1911) experimentally hybridized many species 
of teleosts and found that in the species he tested the 
eggs ofeach species could be impregnated by the sperm 
of any other species. He also determined that the stage 
to which any given hybrid would develop was correlated 
with the nearness of the taxonomic relationship of the 
two species used. Thompson (1935) reported that with- 
in certain groups of fishes hybrids were common and 
tanged from a few to as high as 10 per cent of the pop- 
ulations. 
Hybrid sunfish have receivedthe attention of a num- 
ber of biologists. Hubbs (1920) expressed the opinion 
that Lepomis euryorus McKay was the hybrid of the 
green sunfish, L. cyanellus Raf., and the pumpkinseed 
sunfish, L. gibbosus (L.). Hubbs & Hubbs (1931) val- 
idated this opinion by successfully hybridizing green 
and pumpkinseed sunfishes in aquaria in the laboratory. 
These authors (1932) also established that the name 
L. ischyrus (Jordan & Nelson) was apparently based 
on the hybrid of the bluegill, L. macrochirus Raf., and 
*William F. Childers is Assistant Aquatic Biologist and George 
W. Bennett is Aquatic Biologist and Head of the Section of Aquatic 
Biology, Illinois Natural History Survey. 
William F. Childers 
George W. Bennett* 
the green sunfish. Hubbs & Hubbs (1933) reported that 
“‘aquarium-reared’’ and ‘‘natural’’ hybrid sunfishes 
grew more rapidly than their parent species, were pre- 
dominately of the male sex, and were apparently sterile. 
Luce (1937) successfully produced hybrid sunfish by 
manually stripping eggs from ripe females and milt 
from ripe males into fingerbowls containing small a- 
mounts of water. After the eggs hatched, Luce raised 
some of these hybrids to sexual maturity in aquaria 
in the laboratory. Ricker (1948) and Krumholz (1950) 
produced large numbers of hybrids by placing adult 
males of the bluegill and adult females of the red-ear, 
L. microlophus (Gunther), in ponds containing no other 
fish. Lagler & Steinmetz (1957) produced hybrids by 
placing ripe adult males of one species of sunfish with 
ripe adult females of another species in ponds which 
contained no other fish (pumpkinseed males with blue- 
gill females and bluegill males with pumpkinseed fe- 
males). 
The intrageneric Lepomis crosses investigated by 
the authors mentioned above and the results of these 
investigations are summarized in table 1. Each of the 
Lepomis hybrids except, of course, the ‘‘natural’’ hy- 
brids of Hubbs & Hubbs (1933) was produced by one 
of three methods: (1) isolating a ripe male of one spe- 
cies and a ripe female of a different species in an 
aquarium, (2)manually stripping eggs from ripe females 
and milt from ripe males into fingerbowls, and (3) iso- 
lating adult males of one species and adult females of 
a different species in a pond containing no other fish. 
The environments of the hybrids in the embryonic and 
larval stages probably differed considerably with the 
method used and may have affected the viability, mor- 
phology, and rate of growth of the hybrids. 
METHODS OF PRODUCING HYBRIDS 
In this paper, G refers to green sunfish, B to blue- 
gill, and R to red-ear sunfish. Matings between indi- 
viduals of different species are designated as P] cross- 
es, and the resultant hybrids are designated as F] hy- 
brids, fig. 1. Fp hybrids are those produced by mating 
an F) male with an Fy female. The kind of fish that 
furnished the sperm is always given first; thus, the P 
cross of a male bluegill and female green sunfish is 
designated B x G, and the resultant hybrids are des- 
