10 
Although the largest specimens collected in the study 
area were males, the differences between male and fe- 
male mean standard lengths at various ages were not 
statistically significant. “Thomas (1970:13) also found 
no influence of sex on growth rate. 
DEMOGRAPHY 
Density 
Four specimens of P. phoxocephala were taken in the 
507 square yards of river quantitatively sampled by an 
electric seine as described earlier. The sample contained 
750 fishes, an average of 1.48 fish per square yard (aver- 
age depth 30 cm) and one P. phoxocephala per 169 
square yards. Assuming that, rather than being uni- 
formly distributed in the area sampled, P. phoxoce phala 
mainly occupied the gravelly raceway that constituted 
about one-fourth (127 square yards) of the area, a more 
realistic figure of one darter per 42.3 square yards of 
gravel habitat results. Because of the inefficiency of 
sampling by the electric seine and previous collecting in 
the area, the figure of one darter per 42.3 square yards 
may be rather low. 
At two sites in the Kaskaskia River, Thomas (1970: 
6) found more than 200 P. phoxocephala individuals 
per acre of water, which is one darter for approximately 
24 square yards of water, almost twice the density of 
P. phoxocephala in the Embarras River. However, at 
many other sites in the Kaskaskia River, the number 
of P. phoxocephala individuals per acre was smaller than 
that in the Embarras River study area. 
Composition 
Of the 238 P. phoxocephala collected in the study 
area, 176 (74 percent) were young-of-the-year, 59 (25 
percent) were 1-year-old fish, and 3 (1 percent) were 
2-year-old fish (Table 3). No specimens 3 years old or 
older were examined, and in view of the sharp decrease 
in numbers in each successive age class, it is doubtful 
that in the Embarras River many individuals live to 3 
or more years of age. Of 25 specimens from Boone 
County, Iowa, examined by Karr (1963:232), five were 
3 years and two were 4 years old. 
Fig. 8.—The habitats in the Embarras River 
occupied by P. phoxocephala throughout the 
year. The principal habitat, the gravel raceway, 
is abandoned during the spawning period and 
during the colder months of the year. 
TasBLeE 3.—Distribution of sexes and year classes in Percina 
phoxocephala taken from the study area between August 4, 
1967 and September 20, 1970. 
Number by Year Class 
Sex =i se Dee Total 
Males 98 38 3 139 
Females WP 21 0 93 
Too small to sex 6 ns fe 6 
Total 176 59 3 238 
Considerably more males than females were collected, 
giving a sex ratio of 1.5 males to 1 female. The sex 
ratio of the 170 young large enough to be sexed was 
also skewed in favor of the males, although less than 
that of the total sample (1.4:1). In the small sample 
from the Kaskaskia River that Thomas (1970:14) used 
to illustrate growth rate, there were 23 males and 18 
females (1.3:1). However, much larger samples are 
needed to determine the true sex ratio of these popula- 
tions. 
Although the data in Table 3 suggest that P. phoxo- 
cephala males live somewhat longer than females, 12 
of the 28 two-year-old fish examined for the data shown 
in Fig. 7 were females. If there actually is a skewed 
sex ratio in the population, more males than females 
would be expected in any age class, and this factor 
would obscure any sex influence on longevity. 
The largest specimen examined by us was a /8-mm, 
2-year-old male collected in the Kaskaskia River on 
September 6, 1968. Trautman (1957:543) listed the 
largest Ohio specimen as 4 inches long (approximately 
100 mm total length). 
Migration 
P. phoxocephala exhibited the same annual migra- 
tory pattern as that shown by P. scicra, i.e., a late fall 
emigration from and an early spring return to the gravel- 
ly raceways (Fig. 8). Unfortunately, the habitat to 
which the darters emigrated in winter could not be de- 
termined. Quiet regions of the river, such as sluggish 
backwater areas and pools and the deeper portions of 
HIEMAL HABITAT 
GRAVEL RACEWAYS 
SPAWNING (RIFFLES) 
JUNE JULY AUG. SEPT. OCT. 
