OVARIAN WEIGHT AS PERCENT OF ADJUSTED BODY WEIGHT 
JULY AUG. SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNF 
Fig. 5.—Increase in weight of ovaries in relation to body 
weight from the end of one spawning season to the beginning 
of the next. 
remained between 9 and 24 percent in specimens col- 
lected after late February. 
Between 500 and 2,000 ova were produced by each 
female in one season, but only about 10—50 percent 
reached mature size. If we assume that darters lay all 
the mature eggs, as suggested by Fahy (1954:166) and 
Winn (1958b:181), each female P. phoxocephala lays 
from 50 to 1,000 eggs in one season. The largest number 
of mature ova actually counted was 720 in a 60-mm 
female; the smallest number was 50 in a 45-mm female. 
Karr (1963:235) counted the eggs in six P. phoxoce pha- 
la from Iowa and found a range of 186—365. Large 
females produced more eggs than did small females. The 
mean number of mature eggs in three spring-collected 
1-year-old females examined during this study was 83; 
the mean number in six spring-collected 2-year-olds was 
210. 
Mature eggs stripped from ripe females were trans- 
parent and adhesive, averaged 1.3 mm in diameter, and 
contained one large oil droplet. 
Spawning 
The peak spawning period in 1969 was June 7—14, 
and in 1970, June 5—12. In 1968 high water prevented 
spring collections and presumably delayed spawning, 
TapLe 2.—Differentiation and growth of ova in Percina 
phoxocephala collected in the study area. 
Percent of 
Differentiated Ova 
Estimated by Size Group 
Percent of 
Differentiated 0.1-0.5 0.6-1.0 1.1-1.3 
Collection Date Ova mm mm mm 
October 3, 1967 30 100 0 0 
November 17, 1963 40 100 0 0 
February 23, 1969 80 81 19 0 
April 28, 1968 over 90 75 17 8 
April 28, 1968 over 90 80 g 11 
May 4, 1968 over 90 69 16 15 
May 27, 1969 over 90 a9 24 17 
June 8, 1969 over 90 56 23 2a 
July 18, 1967 over 90 42.0 ig 41 
inasmuch as the spawning habitat (shallow gravel riffles) 
was not available until sometime in July. 
The spawning period for P. phoxocephala in central 
Illinois varies with climatic conditions and presumably 
may peak anytime after late May. Females heavy with 
mature eggs were captured at Greenup in late May in 
both 1969 and 1970, indicating that spawning could 
occur that early in the year under ideal conditions. 
Thomas (1970:8) collected ripe females in early August 
in the Kaskaskia River at about the same latitude as 
that of the Embarras River study area. He noted, how- 
ever, that no ripe males were collected that late in the 
year, and it is highly improbable that spawning would 
occur later than early July in central Illinois. 
The spawning habitat of P. phoxocephala is swift- 
flowing water 15—60 cm (1%—2 feet) deep over gravel. 
Males move in mass into the spawning habitat well be- 
fore the females do and presumably establish territories 
although no actual observations of territoriality were 
made. In 1970 males were common in the shallow water 
along gravel bars as early as May 29. The ratio of males 
to females captured in the shallow water on this date 
was 15:1; on June 5 it was 11:2. The fish spawned 
during the following week and by June 13 all adult 
P. phoxocephala had left the spawning grounds. 
Spawning could neither be observed in the field nor 
induced in aquaria. The morphology and spawning 
habitat of P. phoxocephala suggest, however, that mat- 
ing and deposition of the eggs occur in a manner similar 
to that described for other Percina species (New 1966; 
Loos & Woolcott 1969; Reighard 1913; Winn 1953, 
1958a, and 1958b). 
Juveniles remain in the spawning habitat 2—4 weeks 
after hatching. Several young were collected in the 
shallow water (15—30 cm deep) along a gravel bar in 
the study area where spawning was known to have 0c 
curred 2 weeks before. With the young P. phoxocephala 
(ranging from 19 to 27 mm) in the riffles were two 
young P. sciera (19 and 21 mm) and one young P, 
caprodes (33 mm). Collecting in the shallow riffle areas 
2 weeks later produced no young P. phoxoce phala. 
