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80 CALIFORNIA FISH AND GAME
<br />especially those of riparian zones, are highly modified by agricultural develop-
<br />ment, by alteration of stream banks and channels, and through other direct
<br />influences of early and later settlers (Ohmart, Deason, and Burke 1977).
<br />METHODS AND MATERIALS
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<br />An attempt was made to use fishes from throughout the reach, and from
<br />different seasons, to obtain comprehensive coverage. However, this was real-
<br />ized only for some of the more common species such as carp, Cyprinus carpio;
<br />red shiner, Notropis /utrensis; channel catfish, /cta/urus punctatus,~ largemouth
<br />bass, Micropterus sa/moides; and bluegill, Lepomis macrochirus, where t 1 to 50
<br />individuals were studied each season. Foods of other fishes were studied in
<br />spring through autumn. All rainbow trout, Sa/mo gairdneri, were obtained from
<br />fishermen and from Arizona Game and Fish Department personnel near Davis
<br />Dam. Most smallmouth bass, Micropterus dolomieui, examined were caught by
<br />anglers near Blythe, California. Threadfin shad, Dorosoma petenense,~ flathead
<br />catfish, Py/odictis o/ivaris; yellow bullhead, /cta/urus nata/is; sailfin molly,
<br />Poecilia latipinna; mosquitofish, Gambusia affinis; warmouth, Chaenobryttus
<br />gu/osus; striped mullet, Mugi/ cepha/us (the only native fish taken); and the
<br />mouthbrooder, Sarotherodon mossambica, all were from the reach below
<br />Blythe. Redear sunfish, Lepomis micro/ophus; green sunfish, L. cyane//us; and
<br />black crappie, Pomoais nigromacu/atus, were obtained near Parker and/or
<br />Yuma, Arizona. Specimens taken by hook and line or with various seines were
<br />sacrificed for analysis to avoid prolonged restraint and loss of food items through
<br />continuing digestion which occurs in fishes taken in gill, trammel, and hoop nets
<br />of various sizes and meshes (Minckley 1979).
<br />Food habits were determined by examination of stomach contents under
<br />appropriate magnifications. In species with ill-defined stomachs (e.g. carp) the
<br />anterior few centimetres of digestive tract was examined. Stomachs were ex-
<br />cised from larger fishes, after ligation of the esophagus and pyloric regions, and
<br />preserved in 10% formalin. All stomachs were tagged for later identification.
<br />Small fishes were preserved intact in the field and their viscera removed in the
<br />laboratory.
<br />Data were reduced as "frequency of occurrence," which tends to under-
<br />estimateimportance of large items and over-estimate importance of small items.
<br />However, this technique develops comparative data, expressed as percentage,
<br />among diverse species, and avoids ambiguities of assigned (estimated) "points"
<br />(Hynes 1950) or attempted reconstruction of live volumes of animals from
<br />fragments present (Ricker 1937). Stomach contents were teased apart in water
<br />and identified through use of keys of Edmondson (1959) and Usinger (1956).
<br />Reference collections were used to identify fishes and larger crustaceans.
<br />RESULTS
<br />?.
<br />I~~ General Food Habits
<br />)~ Detritus formed the major proportion of stomach contents of threadfin shad,
<br />~'" red shiner, mouthbrooder, sailfin molly, and striped mullet (Table 1 ), and was
<br />~! common in carp, channel catfish, and yellow bullhead. Most detritus was identi-
<br />fiable asfibrous particles of higher plants, typically aquatic macrophytes. A small
<br />percentage was dark, gelatinous material identical in appearance to gytjja-like
<br />organic depc~
<br />occurrence ~.
<br />bottom. Amo
<br />often include
<br />plankton (Ta
<br />stomachs of
<br />clams, Indic
<br />1969) by th~~
<br />exceed its e
<br />organisms be
<br />mouthbrood~
<br />(or epiphytic
<br />higher plant
<br />plants.
<br />Although r
<br />easily have !~
<br />considerabl`
<br />formed a m~.
<br />Davis Dam
<br />visually-ore.
<br />indiscrimin,~'
<br />mullet. Some
<br />some diatoR
<br />Zooplankt
<br />bluegill incl~
<br />lions in Colc
<br />penstocks in
<br />green sunf~s
<br />near-bottor
<br />might be cc
<br />Benthic ~r
<br />fined, with c
<br />trout from
<br />simuliid dipt
<br />chid trichoF
<br />trichopterar
<br />curved in stc
<br />mids, and
<br />occurrence
<br />ence on bey
<br />which is sup
<br />1948). Yellr
<br />fish ate on
<br />Most me
<br />mids, culici
<br />terrestrial it
<br />insects I Inc
<br />on animal
<br />2--f32s23
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