10 
the rest of the body. The sensory canals on the head 
were present but incompletely pored, and the supra- 
temporal canal was widely interrupted medially. The 
opercular spine was small and weak. The midventral 
specialized scales were not present. 
In a 26-mm male (Fig. 7) collected at the same 
time and place as the 16-mm fish, the body proportions 
were more nearly those of the adult, except that the 
eyes were still relatively large and the fins proportion- 
ally small. Squamation was complete except on the 
nape. The pattern of pigmentation was that of adult 
fish, although less intense. The lateral line was com- 
plete. The head canals were complete and apparently 
fully pored, and the specialized scales were present on 
the midventer. In individuals 31- to 35-mm_ long, 
scales were present on the nape. 
The basic color pattern of the adult was formed 
quite early, but pigmentation re mained subdued 
throughout the first year. It intensified continuously 
thereafter, older fishes always being darker than younger 
ones in any given sample. 
Growth 
Standard length frequencies of specimens taken 
from the study area from August 4, 1967, to July 1, 
eae e442) 
eal, SiG) 
_Cm 2+(18) 
YEARS 
Cm 1+ (23) 
—Cmln 53 (10) 
mln 39-44 (12) 
Cm) 18 (14) 
Cm 16 (23) 
__Cmn 14(28) 
WEEKS 
_Cm «12: (28) 
—_Cm 929) 
_Cmn 7 (24) 
—__COm) 5 (18) 
1OR2Cse 5 Ole 4 Ol OO COM ORE SOME OO BEIOO 
STANDARD LENGTH, mm 
Fig. 8—Growth of Percina sciera in millimeters standard 
length. The vertical line represents mean; horizontal line, 
range; hollow rectangle, one standard deviation to either side 
of mean; solid rectangle, two standard errors to either side of 
mean. Numbers in parentheses are specimens measured. Young 
in the first sample were estimated to be 5 weeks old; other 
samples were aged from the collection date of the first sample. 
1969, indicated rather rapid growth in the species, 
notably during the first few months of life. Presumably — 
growth continues throughout life, but the rate diminishes 
with age. 
The growth data for samples taken from August, 
1967, to July, 1968, (Fig. 8) showed a continuous 
average increase in size, except during late October 
(16 weeks) and November (18 weeks), when the mean 
standard lengths of two collections averaged less than 
those of the early October (14 weeks) collections. 
This reversal, which also occurred in samples from 
November, 1968, is assumed to be the result of an 
emigration of the larger fish from the comparatively 
shallow raceway being sampled to the deeper channel 
as winter approached. 
In all but one sample of young taken in the study 
area, males averaged larger than females. The average 
standard length of darters between 1 and 2 years old 
was 57.5 mm for females and 61.4 mm for males; of 
those between 2 and 3 years old it was 62.3 mm for 
females and 73.3 mm for males. The largest specimen 
examined was a 44-year-old male 108 mm in standard 
length collected November 1, 1968, in the Little 
Wabash River. 
A transition from a predominantly pelagic to benthic 
swimming behavior was noted between young and adult 
dusky darters in aquaria. Young fish were active and 
spent most of their time swimming about and rarely 
resting on the bottom. Older fish, however, were 
usually quiet, occasionally darting about over the 
bottom or actively swimming. 
PHYLOGENETIC RELATIONSHIPS 
Within the subgenus Hadropterus, P. sciera and 
aurolineata are most alike in morphological features 
and least often found together where the ranges of all 
four members of the subgenus overlap. P. nigrofasciata 
appears to be more closely related to P. sciera and P. 
aurolineata than to P. lenticula (Suttkus & Ramsey 
19072138): 
Among subgenera of Percina, Hadropterus appeals 
to be intermediate between the more primitive (Hypo- 
homus, Swainia, Percina) and the more advanced 
(Cottogaster, Ericosma, Imostoma, Alvordius) forms 
but probably is more closely related to the primitive 
subgenera. Primitive characteristics ex hibited by 
Hadropterus include highly pelagic habits, large size, 
high meristic counts, and the modest specialization of 
the midventer row of scales in the males. 
One of the anatomical features considered to be ai 
indicator of phylogenetic position of darters is the 
degree of abatement of the gas bladder (Winn 1958a: 
188). In Etheostoma, bottom-dwelling habits are ac 
companied by a reduction or loss of the bladder. In 
some species of Percina the gas bladder is present but 
small and in various stages of reduction. However, 
is relatively large in P. sciera, indicating little phylete 
