29 
Seasonal Diet of Margined Madtom 
was extremely low during the winter. Overall, low numbers of Plecoptera 
nymphs were consumed. Winter-emerging stoneflies (e.g. Taeniopteryx, 
Strophopteryx , Amphinemoura, and Allocapnia ) were consumed when 
large instars were most abundant in New Hope Creek. 
Our results indicate that the diet of N. insignis is similar to that of 
other species of Noturus (Mayden et al. 1980, Mayden and Burr 1981, 
Burr and Mayden 1982, Miller 1984). Unlike Flemer and Woolcott 
(1966), we did not find any fish remains in the madtoms sampled. 
Seasonal variation in the composition of the diet was observed. We 
believe it is attributable, in part, to seasonal variation in the abundance 
of different prey taxa. For example, Baetis, Simulium, and winter- 
breeding stoneflies were most abundant in the madtom’s diet when large 
individuals of these taxa were most common in the stream. Miller 
(1984) did not observe seasonal variation in the diet of Noturus munitus. 
An interesting trend is apparent when the diet of the madtom is 
analyzed by size class (Table 3). As madtoms increased in size, the 
proportion of chironomid larvae consumed decreased relative to other 
prey. That trend in chironomid consumption, though evident during 
spring, summer, and fall (Table 4), is most pronounced in summer and 
fall. In winter the proportions of chironomid larvae consumed by the 
two intermediate size classes were almost identical; only the largest fish 
had a fairly diverse diet. Chironomids increased in importance for 
intermediate-sized madtoms (61-90 mm) during the winter, when their 
movements were probably restricted by swift currents. In the spring, on 
the other hand, the proportions of chironomids consumed by all size 
classes were reduced. That appears to be a result of the increased 
consumption of Baetis and Simuliidae by all sizes of madtoms, possibly 
as a consequence of increased encounter rates with those taxa. In 
general, though, as madtoms increased in size the importance of 
chironomids in the diet decreased, while the importance of other 
invertebrates, primarily Ephemeroptera and Simuliidae, increased. The 
importance of chironomids as prey for the young of other stream fish 
has been noted by Allen (1941), Scrimgeour (1986), and Weatherley 
(1987). Mayden and Burr (1981), Burr and Mayden (1982), and Miller 
(1984) also noted an increase in the diversity of the diet of other 
Noturus species with increasing size of the fish. 
We have considered three explanations for the more diverse diet of 
large madtoms: (1) small madtoms may be restricted in habitat use by 
piscivorous predators, (2) movement of small madtoms may be restricted 
to areas of reduced current velocity, and (3) the mouths of small 
madtoms are just too small to handle large prey. Because we collected a 
majority of the madtoms in riffles, where largemouth bass, the dominant 
