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" 94 - JOURNAL OF THE ARIZONA-NEVADA ACADEMY OF SCIENCE shad (TL = 95 and 138 mm) which comprised 77% of the gut contents of that individual. A filamentous alga, Cladophora glomerata, was only in catfish from Station A where it had about a 10% frequency of occurrence and accounted for nearly 17 % of the total biomass. Algae were important only the in larger fish (TL>300 mm), where algae occurred in 8857c, of guts and contributed 54% to biomass. The intestinal contents of 20 catfish (TL = 101-322 mm) contained food items of the same nature and proportion as stomachs. One catfish (TL = 256 mm) intestine contained shell fragments of Asiatic clam, Corbicula fluminea. DISCUSSION. -The results of this study compare favorably with others (Table 2, see also Carlander 1969) indicating that channel catfish are both omnivorous and opportunistic. It is notable that my results are most similar to those of Dill (1944) for another California canal. The abundance of Lepidoptera and Trichoptera larvae on concrete surfaces in the Coachella Canal (Marsh and Steinmetz 1981) probably accounts for their predominance as food. Although Lepidoptera larvae appeared to provide a relatively small biomass for channel catfish, their high frequency of occurrence is unusual; I know VOL. 16 of no other studies which have found this insect in catfish diets, nor as an important component in the diet of any North American fish (see Carlander 1969, 1977). Threadfin shad were abundant in the canal (Minckley 1981b) especially at Station A; however, channel catfish made little use of that resource. Kimsey et al. (1957) reported a similar relationship at Palo Verde Lagoon on the lower Colorado River. Asiatic clams were a relatively important food of channel catfish from the Sacramento-San Joaquin Delta, California (Turner 1966) and from the lower Colorado River (Minckley 1981a), yet rare in fish from the Coachella Canal where they were the most abundant benthic invertebrate on natural substrates (Marsh and Steinmetz 1981). As increasing kilometers of earthen canals are lined with concrete in the interest of water transport efficiency, it h.; been hypothesized that populations of invertebrates such a_1 net-spinning caddisflies and aquatic Lepidoptera may increase substantially (Marsh and Steinmetz 1981). These increase may be accompanied by population increases of those cana.. fishes, including channel catfish, which use these insects a..; primary food resource. Such modifications may thus enhanc- recreational fisheries supported by artificial waterways. Table 2. Comparative data on percentage frequency occurrence of foods in channel catfish stomachs. Authority and Locality Present Turner (1966) Jearld and study Dill (1944) Sacramento- Brown (1971) Minckley Coachella Irrigation San Joaquin Delta, CA L. Carl (1981b) Low. Food item Canal, CA Canal, CA <20 cm FL >20 cm FL Blackwell, OK Colorado Riv . Oligochaeta - - - - - 1.5 Mysidacea - - 13.8 13.3 - - Isopoda - 2.6 1.1 - 0.1 - Amphipoda - - 93.9 80.0 - - Decapoda 3.3 - - 20.0 2.9 24.9 Ephemeroptera 17.9 2.6 - - 9.1 - Odonata 64.2 39.5 - - 0.1 - Trichoptera 99.3 47.4 - - - - Lepidoptera 61.6 - - - - - Coleopters - - - - 1.2 - Diptera 70.9 89.5 26.5 6.7 67.2 5.1 Other insects 14.0 - 4.4 6.7 1.2 - Mollusca + - 0.6 20.0 0.1 29.2 Fish 1.3 2.6 - 13.3 12.1 18.9 Fish eggs - - 0.6 - - - Terrestrials + 36.8 - - 0.6 - Filamentous algae 7.9 2.6 - - - - Benthic algae - - - - - 8.0 Plant material + 21.1 - - 1.0 40.9 Detritus - 31.6 - - 4.6 32.9 Other + 2.6 0.6 6.7 - 1.4 Percentage empty 1.3 5.0 10.8 34.7 34.7 16.1 Number of stomachs 153 40 203 23 196 137 Mean fish length (mm) 158 155 121 331 - Range in length 75-415 79-269 40-530 170-840 236-737 ISSUE CARL. Bioli Iowz Volt 431 DILL, Cali JEAR chat Plai 115 KIM S Pro Dor 195 Fis] MAR to b Cal The Albt T erro prol that bett .K If tr. The Hof imp don trac the I infc goo doe