14 
LENGTH OF FISH IN MILLIMETERS 
| a 3 4 
SUMMERS OF LIFE 
Fig. 7.— Growth of P. phoxocephala throughout its life. 
Fish are from the August 3, 1965 rotenone collection at Sulli- 
yan. The sexes are shown separately and actual numbers used 
in the averages for each year-class are shown. 
species, and this species averaged 71.5 mm in_ total 
length at the end of the first year. P. phoxocephala 
were smaller than P. maculata at the end of the first 
year, possibly because the P. phoxocephala bred later 
in the spring. In Boone County, Iowa, Karr (1964) 
found that P. maculata grew faster throughout their 
life span than did P. phoxocephala. The mean calcu- 
lated lengths at the end of the first year were 34.1 mm 
for P. phoxocephala and 34.7 mm for P. maculata. 
My data showed that during their second and third 
years of life, P. phoxocephala grew slightly faster than 
P. maculata. Also, growth for both of these species 
was much faster in the Kaskaskia, where P. phoxo- 
cephala averaged 45.3 mm and P. maculata 50.9 mm 
at the end of the first year. 
Growth for P. phoxocephala was compared at Sulli- 
van and Carlyle. Three-year-old fish showed slightly 
faster growth at Sullivan, but 1- and 2-year-old fish 
were larger at Carlyle. The differences found in 1-year- 
old fish at Sullivan and Carlyle in 1965 were not signifi- 
cant. The growing season was probably somewhat longer 
and spawning earlier at Carlyle, but the Sullivan area 
provided a more favorable habitat for this species. 
The oldest individuals found were two P. maculata 
/ 
a/ 
12 
TKe) 
on | 
oc 
ui 
= 
uJ 
= 
= 
=s0 
= 
= 
x 
w 
rs P caprodes 
iL 80 
ro) 
x 
om 
oO 
rT 
me, Ue) 
\ 2 3 4 
SUMMERS OF LIFE 
Fig. 8. — Growth of P. caprodes throughout its life. F 
are from the August 3, 1965 rotenone collection at Sullive 
The sexes are shown separately and actual numbers used in t 
averages for each year-class are shown. 
collected in August, 1965 at Sullivan which were 
their 5th year of life. No 4-year-old fish were fou 
in any of the other three species. Very few of thi 
Percina live past their 3rd year. 
The population structures of these darters var 
with the species’ abundance and its success in reprod 
tion. Yearly changes in population structure at a stat 
were sometimes quite great, as shown in Tables 2 4 
3. In 1965, the population of P. maculata at Sullis 
was composed of approximately 50 percent young: 
the-year. Further downstream the smaller populati 
of this species were comprised mainly of young (J 
10). Only P. maculata and P. phoxoce phala were ab 
dant enough to permit population comparisons at 
three main collecting stations (3, 6, 9). 
