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INTRODUCED FISHES OF THE LOWER COLORADO 81 j agricultural develop- ~ 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, Corbicuia %/uminea, 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 , r~unctatus,• 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 ra petenense; flathead ! plants. Although much of the algae eaten by fishes in the lower Colorado River could rainbow trout contained ms it h f nata/is; sailfin molly, ^~~uth Chaenobryttus , er e or ot easily have been ingested while foraging considerable volumes of C/adophora g/omerata, 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 ~:h L cyanel/us; 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 ~f food items through pp es spec ga mullet. Some a some diatoms) were found in stomachs of the last two species (Table 1). ~rnmel, 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 ar hs (e carp) the ~ g , p ver rese o Lions 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 ~ might be considered more than trace amounts of zooplankton. . c era removed in the { Benthic invertebrates were present in stomachs of essentially all fishes exam- n larvae almost universally represented. Rainbow ter id di hi ' !rich tends to under- a p ronom fined, with c P trout from below Davis Dam ate about equal amounts of chironomid ap.d ~r~nce 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- ~c-s of animals from s tarred in stomachs of fishes from below Parker Dam. Red shiners ate chirono- low frequency of Th h ~eased apart in water ,nd Usinger (1956) e opterans. ~ mids, and a few ephemeropterans and tric occurrence of chironomids in channel catfish (5.1%) indicated little depend- . r;~~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 l 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- , I Table 1 ), and was ~ mids, culicids, dixidsl?), and undetermined insect groups. About 43% fed on and spiders) and aerial adults of aquatic ants ertebrates (aphids l i i r detritus was identi- ~:-,crophytes A small , , nv a terrestr insects (included with terrestrial insects in Table 1 ). sailfin mollies did not feed . prance to gytjja-like on animal materials lsee, however, Harrington and Harrington 1961). ~--82823