ction of the spinous and soft-dorsal fins. Aging 
month was done by using April, the month of the 
atest breeding activity in the study areas, as 
nth zero. Thus, a darter collected in September 
1 having two scale annuli was estimated to have 
sd 2 years and 5 months. For certain comparisons 
5 
darters were divided into young ( through 12 months) 
and adult (over 12 months) age groups. 
A representative sample of each collection was 
dissected to identify stomach contents and endo- 
parasites and to note the conditions of the gonads. 
Weights of the ovaries of 87 females were obtained 
and recorded as a proportion of the adjusted body 
weight (the specimen minus the ovaries, stomach, 
intestine, and liver) of the female; the weight after 
the removal of the digestive system was used to 
eliminate variations resulting from the weight of re- 
cently ingested food. Mature ova from 18 preserved 
breeding females were counted. 
In addition to specimens collected from the study 
areas during the study period, all E. squamiceps in the 
Illinois Natural History Survey collection were ex- 
amined to ascertain probable spawning periods in 
other localities and other years. Indicators used were 
that males were in extreme breeding coloration and 
that females were heavy with mature ova. 
The relative survival of each year class of the 
two populations was calculated by expressing the 
number of individuals in that year class as a propor- 
tion of the number of individuals in a younger year 
class. 
The breeding behavior and territoriality of darters 
in laboratory aquaria were observed. Stream observa- 
tions had indicated that territories centered naturally 
about large slab stones, and one or more slab stones 
(elevated slightly on small stones) were placed in 
each aquarium. 
HABITAT 
Adults of the Big Creek E. squamiceps population 
showed a distinct difference in their preference in 
habitat (as defined ) from the preference of the Fergu- 
son Creek adult population (Table 1). In Big Creek 
Fig. 2.—(Upper Photo) Slab 
pool in the headwaters of Big 
Creek, Hardin County, Illinois. 
(Lower Photo) Slab riffles in 
Ferguson Creek, Livingston Coun- 
ty, Kentucky. 
