Diagnosis:  The quillback is a much compressed carpsucker, differing from the river carpsucker in having the anterior rays of the dorsal fin greatly elongate in the adult, a deeper body, a produced and squarish snout, and usually more than 37 scales in the lateral line, and in lacking the nipplelike protuberance at the tip of the lower jaw.

Ecology: The quillback is common in creeks, rivers, and some lakes.  In streams it feeds on bottom ooze in pools and eddies of backwaters.  It has a wider range of ecological tolerance than other carpsuckers, occurring in clear and silty habitats and in streams of various sizes.

Distribution: It is statewide in occurrence in Illinois but rather sporadic and uncommon in the southern half of the state.  In northern and much of central Illinois it is widely distributed and abundant in streams of all sizes and in some lakes.

• ICTALURIDAE — North American freshwater catfishes (bullheads)        

        Black Bullhead:

Diagnosis:  The black bullhead is a robust bullhead, uniformly black or olive above and whitish or pale yellow bellow, with squared caudal fin, dusky chin barbels, 16-20 anal rays, a light vertical bar on the caudal peduncle, black interradial  membranes on most fins, and a roughened (but not serrate) rear edge of the pectoral spine.

Ecology: It inhabits lakes, ponds, swamps, and pool habitats of streams of all sizes, particularly those in low-gradient creeks.   Its breeding and feeding habits are simila to those of other species of Ictalurus.

Distribution: The black bullhead is common in all parts of the state.  Yet there is evidence from an examination of the distribution map of new species, that it was formerly even more ubiquitous than it is now.

        Yellow Bullhead:

Diagnosis:  The yellow bullhead is a robust bullhead, olive or brownish above and yellowish below, with a paddle-shaped caudal fin, immaculate white or yellow chin barbles, 24-27 anal rays, a vague dark stripe running through the middle of the anal fin, and a finely serrate rear edge on the pectoral spine.

Ecology: The yellow bullhead is said to be a stream species, whereas the black bullhead is more typically a pond species. The yellow bullhead is the most abundant and most widespread catfish in the state, possibly because it is primarily a creek species and has abundant habitat.

Distribution: It is statewide and common, evidently more so than formerly, since Forbes and Richardson (1908:185) noted that it was then much less common than the black bullhead.

       Brown Bullhead:

Diagnosis:  The brown bullhead is a stoutbodied, olive, yellowish brown, or blueblack above and heavily mottled or marbled along the sides, with dusky chin barbles, a squarish caudal fin, 21-24 anal rays, and large "teeth" on the rear edge of the pectoral spine. 

Ecology: In Illinois, the brown bullhead occurs in clear, well-vegetated lakes.  Its habits are similar to those of other bullheads. 

Distribution: It is reputed to be an extremely hardy and ecologically tolerant species in many parts of its range, but such does not appear to be the case in Illinois.  The species is nowhere abundant but is most often taken in the glacial lakes in the extreme northeastern part of the state, in floodplain lakes along the middle Illinois River, and in swamps of extreme southwestern Illinois.

     Flathead Catfish:

Diagnosis:  The stonecat is a rather slender, slate-colored madtom with a long, keel-like adipose fin separated from the caudal fin by only a notch; the upper jaw projecting beyond the lower; uniform color above or vague blotches of yellowish white; a discrete, small white spot immediately behind the dorsal fin; a long backward extension on each side of the band of premaxillary teeth; and a squarish caudal fin with a whitish margin.

Ecology: It is most abundant in strong riffles of large creeks and rivers, especially in areas having boulders or large flat rocks.  It also occurs in strong riffles over gravel but seems to prefer large rocks.

Distribution: Except for the Wabash river and one record near the confluence of the Kaskaskia and Mississippi rivers, the stonecat is confined to the northern half of Illinois, where it is common and generally distributed in suitable habitat.

Diagnosis:  The brindled madtom is a tan or gray catfish with three bold, broad black saddles, the last one completely traversing the adipose fin, and numerous flecks and mottlings of black or brown on the back and sides; a discrete black spot near the apex of the dorsal fin; a subdistal black vertical band in the caudal fin;  long, keel-like adipose fin separated from the caudal fin by only a notch; the upper jaw projecting beyond the lower; strong "teeth" on the rear edge of the pectoral spine; a paddlelike caudal fin; and a relatively large eye.

Ecology: It occupies clear shallow pools of creeks and small rivers over mixed bottoms of sand, fine gravel, silt, and detritus.

Distribution: The brindled madtom is now restricted to the Wabash-Ohio watershed and, although still general in occurance, it is not abundant.