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Invertebrates Introduction Recent research indicates that several invertebrate taxa are important to larval and juvenile fish. The Chironomidae and the crustaceanss Cladocera and Copepoda are important food for these fish. Grabowski and Hiebert (1988) analyzed stomach contents from many species of fish at different developmental stages. Their work was performed during 1987-88 on the Green River in backwater and riverine habitats from Island Park to Ouray National Wildlife Refuge. They reported that chironomids were by far the most frequently encountered prey in the stomachs of all the fish studied. A study conducted by Marsh and Langhorst (1988) of wild larval razorback suckers diet in Lake Mohave and an adjacent backwater at Arizona Bay found that Cladocera and Copepoda made up a greater frequency of the diet than other available taxa. The study by Marsh and Langhorst, which occurred in a lentic as opposed to the lotic environment studied by Grabowski and Hiebert, also found a greater selection of Cladocera than Copepoda in relationship to availability. A key objective of the present study was to determine the suitability of study wetlands along the Colorado, Green, and Gunnison Rivers as habitat-for rearing endangered fish. Three aspects of habitat suitability are hydrologic regime, chemical environment and food availability. The hydrology and water chemistry variables were discussed above, and this section discusses the availability of food. Bulrush, open water-aquatic and alkali bulrush communities occur in the study area as well as river channel and river backwater communities. All were sampled for invertebrates. The river community was used as a control to compare food resources to those in other communities. Our analyses emphasize the following water column invertebrate groups: 1) Cladocera, 2) Copepoda, 3)~Chironomidae, 4) all other insects less the Chironomidae, and 5) all other invertebrates which include Gastropods, Cnidaria, Nematoda, and Protozoa. Taxonomic divisions presented for benthic invertebrates are: 1) Chironomidae and 2) other invertebrates which include Gastropods, Nematoda, Odonata, Hemiptera, Ephemeroptera, Coleoptera, and Culicidae. Water column invertebrate data is typically reported as number L'1 while benthic invertebrate densities are typically reported as number m'Z. For the present study benthic data were also converted to L'1 so that the water column and benthos could be compared. When applicable two Y axes are displayed on graphs to include both number L'1 and number m'Z for benthic invertebrates. 32