28 
Robert P. Creed, Jr., and Seth R. Reice 
Margined madtoms consumed a wide variety of prey (Table 2). A 
vast majority of the prey were benthic, but some terrestrial prey were 
consumed. We assume that the terrestrial prey were encountered on the 
stream bottom because madtoms were always observed on or in the 
bottom. Of the benthic prey, immature aquatic insects in four orders 
dominated in the diet (93.8%); these orders were Diptera, Ephemeroptera, 
Trichoptera, and Plecoptera. 
Dipterans, especially chironomid larvae, were the predominant 
prey in the diet except in the spring (Table 2). Chironomids were found 
in all but 2 of the 51 madtoms that contained food in their guts. The 
mean number of chironomids consumed per fish in the fall and summer 
was about the same. The number of chironomids eaten was lowest in 
the winter, which appears to be a result of reduced feeding activity by 
members of the 31-60 mm size class of madtoms, perhaps as a result of 
the strong currents present on those dates. A majority of the prey (67%) 
were consumed by large fish ( >90 mm) during the winter. As discussed 
below, large madtoms consumed fewer chironomids than did small 
madtoms. Reduction in the number of chironomids consumed in the 
spring appears to have a different explanation. We observed dense 
aggregations of large instars of Baetis (Ephemeroptera), prior to their 
emergence in the spring, on the upper surface of many rocks. Encounters 
between madtoms and Baetis probably increased at this time of year. 
Increased feeding on Baetis probably led to reduced feeding on 
chironomids in the spring. Indeed, there was an inverse relation between 
the numbers of Baetis and of chironomids in the guts of the 12 madtoms 
collected in the spring (r = -0.47, Pearson product -moment correlation). 
Simulium spp. were also observed to emerge in the spring, the season 
when large instars of this genus are probably encountered most frequently 
by the margined madtom. Simulium pupae were found in the madtom 
gut only in the spring. 
Ephemeropteran nymphs other than Baetis were also important in 
the madtom’s diet (Table 2). Heptageniid nymphs were found in the gut 
throughout the year, with a peak in the summer. About half as many 
ephemeropterans as dipterans were consumed over the entire year. 
However, in terms of prey biomass, it is likely that Ephemeroptera often 
contributed at least as much as Diptera, if not more, to the madtom’s 
diet. In the spring Ephemeroptera outnumbered Diptera and probably 
contributed more biomass to the diet as well. 
There were few apparent trends in the consumption of trichopteran 
larvae (Table 2). However, consumption of Hydropsychidae and 
Hydroptila was greatest in the summer. Most Chimarra were consumed 
during the summer and fall. The total number of Trichoptera consumed 
