16 
The small number of young P. phoxocephala in the 
Sullivan area in 1965 appeared to be the result of 
high waters during the breeding season. In the Carlyle 
area there were more P. phoxocephala adults than 
young. Part of the population here may have repre- 
sented an influx from more favorable areas. Reproduc- 
tion was poor in this section of the river and mortality 
of young may have been high. 
P. phoxocephala in the Vandalia area may have 
spawned before the floods occurred in early June of 
1965. This was the only area where reproduction was 
successful for this species in 1965. 
LIMITING FACTORS 
Stream size is an important factor in the distribution 
and abundance of the four darters in this study. P. 
maculata is generally most abundant in small rivers. 
Larimore & Smith (1963) found for Champaign County, 
Illinois, that this species reached its greatest abundance 
‘n streams with 4-8 square miles of drainage. P. phoxo- 
cephala and P. caprodes are found most abundantly 
in moderate-sized rivers. Probably the rifle-pool ratio 
of a moderate-sized river plus a variety of habitats make 
this size of stream most favorable. P. shumardi is gen- 
erally limited to large rivers. 
Stream gradient also appears to be an important 
factor. P. maculata, P. phoxocephala, and P. caprodes 
all reach their greatest abundance in the area from 
Sullivan to Shelbyville where the gradient is one of the 
highest in the river (Fig. 3 and 4). 
Type of bottom may be an important limiting 
factor, particularly during the breeding season. Winn 
(1958a, 1958b) found that both P. maculata and P. 
caprodes used sand and gravel in which to lay their 
eggs. Long stretches of silt bottom pools (such as at 
stations 8 and 12, Fig. 2) in the middle and lower 
sections of the Kaskaskia probably limited the distribu- 
tion of these darters. 
The timing of floods also is a limiting factor. Starrett 
(1951) found that the usual high river stages in May 
and June limited the abundance of early spawning 
species in the Des Moines River and perhaps postponed 
spawning of some species of fish. The effects of the 
time of floods on reproduction are shown in slablesa. 
Floods also mean high turbidity and possible destruction 
of eggs during the breeding season. 
Competition may be important in limiting numbers 
of individuals, particularly at high population levels. 
Food analyses of the freckled madtom, Noturus nocturnus 
and of young channel catfish, Ictalurus punctatus, indi- 
cate that during the summer they may be competing 
with P. phoxocephala not only for food but for space 
in the limited riffle areas at Carlyle. 
Human alteration of the river has apparently affected 
at least the local distribution of these darters. Dredging 
and straightening of the channel has occurred in the 
headwaters and is now being carried out in the lower 
river. Carlyle Reservoir was partially filled before the 
completion of this study and the Shelbyville Reservoir 
was scheduled for completion later in 1970. Pollution 
is important at times throughout the length of the 
river. Industrial pollution from a chemical plant near 
Tuscola has occasionally killed fish for many miles 
downstream. Pollution fram fertilizer companies has 
also been responsible for a few fish kills. All of the 
above factors have affected the abundance of Percina 
in the area of our studies. 
PREDATION AND PARASITISM 
No evidence of predation on these darters was 
found in the Kaskaskia River. Many stomachs of preda- 
tory fish were examined, including the largemouth bass, 
Micropterus salmoides; black crappie, Pomoxis nigro- 
maculatus; white crappie, Pomoxis annularis; green 
sunfish, Lepomis cyanellus; rock bass, Ambloplites rupe- 
stris: and grass pickerel, Esox americanus; and the only 
darters found were a few specimens of the johnny 
darter, Etheostoma nigrum. 
Two species of external parasites were found on 
three of the Percina studied. These included a smal 
leech, Illinobdella moorei (?), and the copepod parasite 
Lernaea sp. There appeared to be very few interna 
parasites although a few nematodes were found in the 
stomachs. 
The incidence of external parasites (excluding smal 
trematodes) appeared to increase toward the end o 
the summer and early fall. No parasites were fount 
on darters during the spring, but in the August, 196: 
collection with rotenone at Sullivan 11 percent of th 
P. maculata, 15 percent of the P. phoxocephala, and 2: 
percent of the P. caprodes were affected with externa 
parasites. Most darters had from one to four leeche 
on the caudal fin, although a few leeches were als 
found on the pelvic, pectoral, and anal fins. Copepo' 
parasites were much less. common and were usuall 
found at the base of the soft dorsal fin. 
No parasites were found on darters collected 1 
the lower river. 
Copepod parasites appeared to do the most damag' 
as areas of the back where these parasites were foun 
were often soft and infected. Very little external har 
was done by leeches, although some fins were slight 
damaged. 
HYBRIDIZATION 
In the Kaskaskia River, hybridization appeared 
be very rare between members of the genus Percin 
However, in the 1965 rotenone collection from 1 
Sullivan area, two individuals were found which we 
hybrids of P. maculata x P. phoxocephala. Their iden 
fication was verified by Milton B. Trautmamges Oh 
State University, and they are now in the Ohio Sta 
collection (catalog number OSM 14019). 
The two hybrids belonged to two different yeé 
classes, The first individual was 63 mm in leng' 
