deserted their nests and rushed into the nest occupied 
by the spawning pair. A wild melee followed, during 
which males fought with each other and attempted to 
gain control of the female. The female hastily retreated 
toward deep water. A short time after the female had 
gone, the invading males returned to their own nests. 
When the nests in this pond were examined, approx- 
imately 9 out of 10 of those containing eggs had eggs 
scattered outside as well as inside the nests. All of 
the eggs which were outside the nests appeared to be 
covered with fungi, and most of the eggs in the nests 
were similarly infected. Noninfected eggs were col- 
lected from several nests and moved into the laboratory; 
none of these eggs hatched. 
The attacks on spawning pairs by males could limit 
the production of an Fy generation in one or more of 
the following ways: 
1. Females could be prevented from spawning 
until the eggs which they contained were overripe and 
hence nonviable. 
2. There might be lack of synchronization in 
the release of spermatozoa and eggs. Sunfish sperm- 
atozoa are capable of fertilizing eggs for a very short 
period of time, probably less than 60 seconds under 
natural conditions, after they are released into the 
water. 
3. The presence of large numbers of fungus-in- 
fected eggs outside of the nest could lead to the pro- 
duction of so many fungus spores that a high incidence 
of fungus-infected eggs within the nest would result. 
It is interesting to note that there is a fairly close 
relationship between the success of certain P, field 
crosses in producing an Fy generation and their Fy 
hybrids in producing an F> generation. Both R x G and 
G x B crosses produced large numbers of Fy hybrids 
each time these crosses were tried. The RG and GB 
hybrids produced large F> generations. The production 
of a large F> generation was not related to whether 
the F; hybrids were produced from field crosses or lab- 
Oratory crosses, as both crosses produced large F2 
generations. 
GROWTH OF F] HYBRID SUNFISH 
Growth was recorded for each of the six types of Fy 
hybrids that were produced at various times during the 
summers of 1956-1959 and placed in ponds containing 
no other fish. Varying numbers of fry had been placed 
in the ponds, which differed in size, depth, shape of 
basin, and fertility. Population densities of F, hybrids 
usually were considerably below those in ponds occu- 
pied by their parent species. Thus, no valid compari- 
| sons in growth rates could be made between the vari- 
ous hybrids in these ponds, or between the hybrids 
and their parent species. The observed growth of one 
population of each hybrid sunfish type has been sum- 
marized below. 
RB Fy Hybrids. — Approximately 2,500 (1,000 per 
surface acre) 1-day-old free-swimming fry were placed 
in a 2.6-acre pond on August 14, 1956. When this pond 
was drained on June 11, 1957, after 10 months (about 
4 of which were warm enough for fish growth), it con- 
tained 463 hybrids ranging in length from 3.4 to 4.4 
inches and averaging 4.0 inches. On that date, 102 of 
these hybrids were placed in a 0.05-acre pond. This 
pond was drained on July 2, 1958, after a little more 
than a complete growing season, and 92 hybrids were 
collected; they averaged 5.3 inches and ranged from 
3.8 to 5.9 inches in total length. 
BR Fy, Hybrids. — Approximately 1,100 (1,200 per 
surface acre) l-day-old free-swimming fry were placed 
in a 0.9-acre pond on May 24, 1957. On October 12, 
1957, after about 4.5 growing months, hardware cloth 
wire traps were set in this pond, and 40 hybrids were 
captured. These hybrids averaged 4.7 inches and ranged 
in length from 3.6 to 5.4 inches. They averaged 0.082 
pound in weight and ranged from 0.035 to 0.100 pound. 
All 40 fish were returned to the pond. On July 28, 1958 
(after 1 year and 2 months), 67 hybrids, which ranged 
in length from 5.4 to 6.9 inches and averaged 6.4 inches, 
were trapped and removed from this pond. The pond 
was treated with rotenone on September 23, 1958, and 
43 additional hybrids were collected. After about two 
growing seasons, these hybrids averaged 7.4 inches 
and ranged in length from 6.2 to 8.3 inches. Average 
weight was 0.35 pound. 
GR Fy Hybrids. — A 0.1-acre pond was stocked on 
May 17, 1957, with approximately 1,000 (10,000 per 
surface acre) l-day-old free-swimming hybrid fry. One 
hundred twenty-eight hybrids were trapped and removed 
from this pond on July 7, 1958, after 1 year and 2months. 
At that time these hybrids ranged in length from 3.8 
to 4.9 inches and averaged 4.4 inches. On August 15, 
1958, 200 additional hybrids, which ranged in length 
from 3.9 to 5.1 inches and averaged 4.7 inches, were 
removed from this pond. On July 29, 1959, when the 
fish were about 2 years old, the population was again 
sampled by trapping. Fifteen hybrids were captured 
and returned to the pond. These fish averaged 7.7 
inches and ranged in length from 7.3 to 8.2 inches. 
They averaged 0.41 pound in weight and ranged from 
0.30 to 0.47 pound. 
RG Fy Hybrids. — A 0.9-acre pond was stocked on 
June 11, 1956, with approximately 1,300 (1,400 per 
surface acre) free-swimming hybrid fry. On June 27, 
1957, 79 hybrids, which averaged 5.0 inches and ranged 
in length from 4.1 to 5.8 
traps and then returned to the pond. During the period 
inches, were captured in 
