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500 THANS, AMER. FISH, SOc., 1969, NO.2 202 ---1 400 I / I I ~ ROBUSTA ROBUSTA---I I I I I I I I / I I I I f f I I I / I / I I / I .- .-; ~Q., ~ ~ '" ~ <( a: 300__ Cl w ~ >- o o lD -' L 200 300 TOTAL BODY LENGTH - MM FII;IJlII; R-Length.weight relali",.,hip, Colorado chuh (G. r, el{'gans and G, r. rolJlJsta), Green Hi\'eL FOOD HAnITS Colorado Squ~wfi$h The Colorado squawfish is generally recog- nized as a carnivore because of its great size, large mouth, and large pharyngeal teeth, It has been reputed to take artificial lures as \\'1'11 as fish, mice, birds, or rabbits as bait (Beckman, 1952), but no detailed food habits studies have been published. Stomachs from ]<)g squawfish ranging from 15 10 598 mm were analyzed in the prescnt study (Tablc 6). Cladocerans, copepods, and chironomid larvae were important food items for squaw- fish lip to 50 1111n lotal length Dnl were not found in larger fish, Utilization of insects increased up to a fish length of 100 mm after '. which fish became the major food item. Fish were the only food item found in stomachs of squawfish over 200 mm long. The smallest squawfish containing fish was 50 mm in length, The fish species found most often in squawfish stomachs was the redside shiJJl~r, but most fish remains were unidentifiable, Concurrent with increased fil:'h utilization i I 400 was an increased fn:llllcncy of empty stOIll- achs, Thirty-nine percent of the stomachs from squawfish over 200 mm long were empty. The increased percentage of empty stomachs in larger fish was probably due to more sporadic feeding of these pisciv- arous fish. No seasonal or geographic changes in diet were apparent. Bass tape;. worms, Proteocephalus ambloplites, were found in 65 percent of stomachs from squaw- fish longer than 200 mm. Dotson (unpublishcll data, Utah State Di- vision of Fish and Game, Salt Lake City) found that the majority of slomachs from 73 Colorado squawfish taken in 1960 and 1961 just below Flaming Gorge damsite were empty, and that fish were the main food item of squawfish 390 to 628 mm long. Thompson (1959) reported that the north- ern squawfish in the lower Columbia River was omnivorous, and that its diet depended upon availability of various items. Norlhem squawfish less than 203 mm long fed mainly upon inserts; those 203 to 279 mm fed mostly on insects and fishes; and those longer than 279 mill fed mostly on fishes and crayfi"hes, Colorado Chub Stomachs from 307 Colorado chuhs IS to 290 mm total length were analyzed (Table 7), Chironomidae larvae and Ephemeroptera nymphs were the most ahundant food itelll~ in the smaller fish, As they grew, Colorado chubs consumed a greater diversity of food ilellls, including aquatic and terrestrial in- sects, Principal food items of fish over 200 mm long were terrestrial insects-mostly adult beetles, grasshoppers, and ants-which were commonly found floating on the surface. Chubs were often seen feeding on surface drift material consisting of terrestrial insects and planl dehris. Plant dehris commonly found in stomachs included leaves, stems, seeds, woody fragments, and horsetail (Eqnisclum) otems, Fish longer than 200 mm were separated into the two taxa, the roundtail and bOllytaiL Eight percent of the roundtail stomachs con- tained fish remains, while no fish remains were found in bony tail stomachs. Colorado chuhs shorter than 200 mm containing fish remains were all identified as roundtails.