omposition progressed from one dominated by dipteran 
arvae to include substantially greater portions of the 
arger mayfly and caddisfly immatures (Fig. 10). The 
mallest specimen (19 mm) available for dissection con- 
ained one mayfly naiad. Aquarium-held darters fed 
eadily on a variety of foods, including fish and shrimp 
lesh, earthworms, snails, isopods, and tadpoles of Pseud- 
crts trisertata. 
Some geographic variation in diet is to be expected, 
Ithough other reports on the food of P. phoxocephala 
ave indicated basically the same composition. In a 
udy conducted in Iowa, Karr (1963:234) found may- 
ies to be the most common food organisms, with dipter- 
n and caddisfly larvae constituting the remainder of 
re diet. Additional items encountered include dragon- 
y naiads and water boatmen (Forbes 1880:23: Forbes 
Richardson 1920:286; Cross 1967:293). 
INTERACTIONS WITH OTHER ORGANISMS 
ompetition 
Observations of P. phoxocephala and P. sciera for 3 
vars revealed no overt competition between them or 
ith any other coinhabitants. However, covert compe- 
tion among species is more difficult to discern, and in 
Id studies can only be suggested in terms of similarities 
| life histories and niche requirements. P. sciera and 
_ phoxocephala share certain ecological characteristics 
.g., similar diets, habitats, breeding habitats) in the 
mbarras River, and competition between them (and 
rhaps with other species) may intensify to the point 
population limitation in certain seasons of the year. 
or example, food may become limiting in winter. 
edation 
No evidence of predation on P. phoxocephala was 
und in the study area. Concurrent with the life-history 
idies of the darters, an investigation was conducted 
| the feeding habits of the most abundant large predator 
13 
in the river, Micropterus punctulatus (Smith & Page 
1969). The only darter remains encountered as food 
items were those of Etheostoma nigrum. Thomas (1970: 
16) also found no evidence of predation on P. phoxo- 
cephala. 
Parasitism 
During the summer and fall, adult and young darters 
were often parasitized by a small leech, identified by 
Dr. Marvin C. Meyer as Piscicolaria reducta Meyer 
(Piscicolidae). Darters with leeches attached were col- 
lected from late June into November; more than half 
of those collected in October and November were para- 
sitized by one to eight leeches of various sizes. Attach- 
ment was usually to the caudal fin, sometimes to the 
caudal peduncle or a pectoral fin. In some cases fin 
rays showed slight damage. 
Of 45 P. phoxocephala individuals dissected for food 
analysis, one had one small nematode in its intestines, 
and another had three nematodes. Another darter of 
this species from Henry County, IIl., had two small acan- 
thocephalans in its intestines. 
Hybridization 
The only literature report known to us of natural 
hybridization involving P. phoxocephala is that by 
Thomas (1970:16) on two specimens of Percina macu- 
lata x P. phoxocephala hybrids from the Kaskaskia River 
at Sullivan, III. 
SUMMARY OF LIFE-HISTORY DATA ON 
P. PHOXOCEPHALA AND P. SCIERA 
A comparison of the life histories of P. phoxocephala 
and P. sciera reveals a few ecological and demographic 
differences and many similarities (Table 5). The differ- 
ences reflect divergent specialization. The similarities are 
due, in part, to the relatively close relationship between 
the two darters and to the fact that both species were 
investigated in the same study area. 
Tasre 5.—Summary of life-history information on Embarras River populations of Percina phoxocephala and P. sciera.* 
Characteristic 
P. phoxocephala P. sciera 
incipal habitat 
awning habitat 
Gravel raceways of moderate-sized rivers 
Gravel rifles 15-60 cm deep 
Gravel raceways of moderate-sized rivers 
Gravel rifles 30-90 cm deep 
ibitat of juveniles 
© at reaching sexual maturity 
€ at reaching sexual maturity 
xual dimorphism in spring 
ceding tubercles 
imber of mature ova counted 
scription of egg 
ual peak spawning period 
rritoriality 
ult morphology nearly complete 
luence of sex on growth rate 
ngevity suggested by study 
luence of sex on longevity 
ximum size suggested by study 
« ratio among young 
grations 
ncipal diet 
Gravel riffles 
1 year 
Gravel riffles 
1 year 
Males about 40 mm; females about 40 mm 
Slight in pigmentation 
Absent Absent 
50-720 80-196 
1.3 mm in diameter, transparent, adhesive 1.5 mm in diameter, transparent, adhesive 
Early June Early June 
Probable during spawning season Probable during spawning season 
At 3 weeks At 3 weeks 
None Males grow faster than females 
2+ years 4+ years 
Males 2+ years; females 2+ years Males 4+ years; females 3+ years 
78 mm 108 mm 
1.4 males: 1 female 1.1 males: 1 female 
Breeding; hiemal 
Aquatic insect immatures 
“Supportive data in Page & Smith (1970). 
Males about 50 mm; females about 40 mm 
Pronounced in both pigmentation and size 
Breeding; hiemal; tributarial 
Aquatic insect immatures 
