siderably below the carrying capacities of the ponds. 
Intraspecific and interspecific competitions were low, 
and the fish grew at rates approaching the optimum for 
their respective environments. 
Green Sunfish vs. BG Fj Hybrids. — On June 3, 
1958, a very small (0.02 surface acre) rearing pond 
was stocked with 1-day-old, free-swimming, laboratory- 
produced green sunfish fry. Another rearing pond of 
the same shape and size was stocked on four different 
dates (May 26, June 3, June 10, and June 18, 1958) 
with l-day-old, free-swimming, laboratory-produced BG 
Fy hybrid fry. On July 10, 1958, both ponds were seined, 
and 171 green sunfish, which averaged in total length 
approximately 0.75 inch, and 171 BG Fy hybrids, which 
averaged in total length approximately 1.0 inch, were 
removed from the rearing ponds and placed in an 0.8- 
acre gravel pit pond, fig. 6, that contained no other 
fish. 
Ten months later (but only 4 months during which 
waters were warm enough for fish growth) the fish pop- 
ulation in the gravel pit pond was censused by trapping 
and rotenone poisoning. All of the fish recovered were 
individually measured, weighed, and sexed. Statistics 
on this population are shown in tables 5 and 6. 
The BG Fy hybrid and green sunfish males had in- 
creased in length at approximately the same rates. The 
hybrid males averaged 0.4 inch longer than the green 
sunfish males. However, as the hybrid sunfish aver- 
aged approximately one-fourth of an inch longer than 
the green sunfish when the pond was stocked, the length 
advantage of the hybrid males may not be significant. 
The BG hybrid sunfish males between the lengths of 
4.8 and 5.7 inches weighed considerably more than the 
green sunfish males of similar sizes. The BG hybrids 
were much deeper bodied than the green sunfish. 
Population density of the fish in this pond was low. 
At the time the experiment was terminated, the pond 
contained only 28 pounds of fish per acre. In the past 
this pond had supported considerably more than 100 
pounds of sunfish per acre. Intraspecific and inter- 
specific competitions between the fish in this pond 
were very low, and the fish had grown at extremely 
rapid rates. 
The results of this experiment indicate that under 
low population densities there is not much difference 
between the growth potentials of BG F] hybrids and 
green sunfish during the first year. Under high pop- 
ulation densities, the hybrid sunfish might grow faster 
than the parent types because of a superior ability to 
compete for food and space. 
gee 1 patty 
ees ‘a, wy a, ; 
He Flan 
_ Fig. 6. — An 0.8-acre gravel pit pond that was stocked with equal numbers of green sunfish and BG F, hybrids of similar 
sizes. 
