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~ e e June 1990 Tyus and Nikirk-Abundance, growth, and diet of lctalurus punctatus 195 TABLE 2-Continued. 22 11 15 Average total length at annulus formation' 18 19 12 13 14 16 20 21 17 395 377 428 370 388 408 352 371 386 434 364 384 403 418 429 412 433 456 474 493 491 421 450 489 514 535 554 579 396 414 430 450 474 506 530 672 507 532 551 578 603 625 644 663 689 722 740 756 378 401 419 450 484 532 572 667 689 722 740 756 6.0 8.7 13 18 28.4 45.9 61.8 4.5 56 39 27 19 12 7 5 2 . in that location, as previously reported by Banks (1964). Larger, more predacious channel catfish may experience difficulty in capturing fish in the Green and Yampa rivers. Only the largest individuals contained fish remains (average TL = 392 mm, n = 28), and whole fish were found in only 12 stomachs (average TL = 446 mm). Fish species identified in stomach contents included channel catfish (n = 9), suckers (n = 2), sculpin, Cottus sp. (n = 1), and speckled dace, Rhinichthys osculus (n = 1). Our inspection of stomachs could have missed partially digested larvae or postlarvae, but some stomachs (n = 4) contained fish eggs. Al- though some of the fish containing fish remains no doubt consumed the prey, the presence of large fish bones, including vertebrae, in relatively smaller-sized channel catfish indicated that many of the catfish were scavenging. The presence of large carp scales in 10 individuals but no other fish parts, suggests some scale-feeding behavior, as reported for marine catfish by Szelistowski (1989). Piscivory only in larger catfish contrasts with other studies reporting piscivory by smaller (50 to 200 mm) individuals (reviewed by Car- lander, 1969). The low incidence of piscivory we found may have been due to low prey availability or other factors such as temperature or turbidity regimens. High turbidity may limit the ability of channel catfish to capture fish as prey, and turbidity ef- fects on catfish suggested by Davis (1959) and T. M. Lynch and D. G. Lemons (in litt.) may also apply to the Green River, in which the sediment load fluctuates from 19 to 66,000 mg/l and the suspended load from about 110 to 1,700 mg/l (ReMilliard et al., 1988). Layher and Maughan (1985) reported optimal water clarity for channel catfish as < 30 mg/l (reported in Jackson Tur- bidity Units). The variety of bottom foods in many channel catfish stomachs (miscellaneous food category in-