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INTRODUCED FISHES OF THE LOWER COLORADO 81 j agricultural develop- 1 organic deposits along the channel and in backwaters of the river. A liberal itivores indicated direct feeding from the f d t h through other direct ynd Burke 1977) r e s o occurrence of sand in stomac bottom. Amorphous detrital materials in stomachs of carp and channel catfish . often included unicellular algae, some of which was likely recorded as phyto- plankton (Table 1). The high incidence of Asiatic clams, Corbicula (luminea, in the reach, and from hi l - stomachs of these fishes, and field observation of carp feeding upon and among robable use of pseudofeces of the mollusk (Prokopovich di i t l )wever, t s was rea - carp Cyprinus carpio; es p n ca ams, c 1969) by the fishes as food. This material, bypassed by a clam when particulates , nunctatus,• largemouth exceed its capacity for ingestion, includes a large percentage of detritus, plus in stomachs of sailfin molly and it t D ;, hirus, where 11 to 50 fishes were studied in r us e organisms bound in a mucoid secretion. mouthbrooder was associated with the high frequency of occurrence of benthic i were obtained from (or epiphytic) algae, and in the case of the latter, with substantial amounts of razed within beds of aquatic often h fi h f personnel near Davis g es s ese t higher plant tissues. Both o mined were caught by ,a petenense; flathead ! plants. Although much of the algae eaten by fishes in the lower Colorado River could rainbow trout contained ms it h f natalis; sailfin molly, -)uth Chaenobryttus , er e or ot easily have been ingested while foraging considerable volumes of Cladophora glomerata, a large filamentous alga that , fish taken); and the formed a major component of organic drift observed and caught on nets near be taken as an innate feeding response by l f )m the reach below i,h L cyanellus; and gae may ting a Davis Dam. Dri visually-oriented fishes such as hatchery-reared trout, or may be consumed , . near Parker and/or indiscriminately by facultative planktivores such as threadfin shad and striped eared to be true phytoplankters (desmids and that a i l l !', various seines were of food items through pp es spec ga mullet. Some a some diatoms) were found in stomachs of the last two species (Table 1). irnmel, and hoop nets Zooplankton in stomachs of rainbow trout, threadfin shad, red shiner, and ristics of limnetic popula- t h d arac e s c bluegill included cladocerans and copepo resumably having been entrained through rvoirs Ri d »,ach contents under achs (e carp) the g , p ver rese o tions in Colora penstocks into the channel. Zooplankters in stomachs of carp, largemouth bass, . . Stomachs were ex- green sunfish, and black crappie also included ostracods and thus included trout and shad contained what Onl eans t i I pyloric regions, and 'r later identification y . ac crocrus near-bottom or benthic m i might be considered more than trace amounts of zooplankton. . sera removed in the { Benthic invertebrates were present in stomachs of essentially all fishes exam- n larvae almost universally represented. Rainbow ter id di hi !)ich tends to under- a p ronom ined, with c P trout from below Davis Dam ate about equal amounts of chironomid and rtance of small items. simuliid dipteran larvae and also contained a substantial frequency of hydropsy- ephemeropteran nymphs, fed on chironomids r C l ,_ssed as percentage, estimated) "points" , p a arvae. chid trichopteran ? trichopteran larvae, and a few odonate naiads. The last three groups only oc- V's of animals from s curred in stomachs of fishes from below Parker Dam. Red shiners ate chirono- low frequency of Th h teased apart in water Ind Usigger (1956) e opterans. mids, and a few ephemeropterans and tric occurrence of chironomids in channel catfish (5.1%) indicated little depend- . w,r crustaceans. ence on benthic insects. No other insect groups were used by channel catfish, which is surprising in light of findings in other streams (e.g. Bailey and Harrison 1948). Yellow bullheads used chironomids extensively, but young flathead cat- is of threadfin shad fish ate only large odonates and trichopterans. Most mosquitofish examined had eaten tiny, soft-bodied larvae of chirono- , (Table 1), and was mids, culicids, dixidsl?), and undetermined insect groups. About 410% fed on and spiders) and aerial adults of aquatic ants ertebrates (aphids l i i t detritus was identi- ,acrophytes A small , , nv a terrestr insects (included with terrestrial insects in Table 1 ). Sailfin mollies did not feed . trance to gytjja-like on animal materials (see, however, Harrington and Harrington 1961). 2--82823