30 Robert P. Creed, Jr., and Seth R. Reice 
Table 3. Contribution (percent) of major prey taxa to the diet of four size 
classes of margined madtoms. a 
Prey taxon 
Size class (mm) 
<31 
(N = 1) 
31 - 
(N = 
60 
18) 
61 
(N 
§ S 
1 II 
91 - 
(N = 
120 
16) 
Diptera 
Chironomidae 
94.4 (17) 
73.1 
(32.9) 
35.9 
(14.4) 
26.4 
(7.9) 
Simuliidae 
- 
0.7 
(0.3) 
3.0 
(1.2) 
18.7 
(5.6) 
Other 
- 
3.2 
(1.4) 
4.7 
(1.9) 
2.5 
(0.8) 
Ephemeroptera 
Baetis 
- 
7.6 
(3.4) 
25.3 
(10.2) 
19.5 
(5.8) 
Heptageniidae 
5.6 (1) 
2.8 
(1.3) 
8.7 
(3.5) 
9.4 
(2.8) 
Other 
- 
0.4 
(0.2) 
1.4 
(0.6) 
3.2 
(0.9) 
Trichoptera 
- 
6.7 
(3.0) 
8.7 
(3.5) 
6.7 
(2.0) 
Plecoptera 
- 
2.6 
(1.2) 
3.0 
(1.2) 
6.1 
(1.8) 
Miscellaneous 
- 
2.9 
(1-3) 
9.3 
(3.8) 
7.6 
(2.3) 
a Mean number of prey individuals of 
shown in parentheses. 
each 
taxon < 
:onsumed 
per fish are 
piscivore of New Hope Creek, are absent, the first explanation seems 
inadequate. In addition, because madtoms are active primarily at night 
and bass feed primarily during the day, predation risk would probably 
be low for all size classes of the madtom. We did not directly measure 
the swimming ability of madtoms under different current regimes. 
However, two pieces of indirect evidence lend support to the idea that 
the movement of small madtoms is influenced by current velocity. First, 
both the total and mean number of prey consumed were lowest in the 
winter, a period of higher than average discharge and of frequent 
flooding (Reice 1981; Creed, personal observation). Most of the prey 
consumed during the winter were eaten by the large madtoms, the only 
size class also to have a fairly diverse diet. Second, Simulium and 
Baetis, which composed about 38% of the diet of madtoms >90 mm 
