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Habitat Overlap Habitat overlap between five fish species in the fall of 1980 was examined at kilometer 424 of the Green River using multiple discriminant analysis. ,,,One discriminant function (DF) accounted for 82% of the among species variance observed in species microhabitats (Fig. 3). Water velocity was the environmental variable which made the greatest contribution`? th toe observed separation ±Letsi en s'ert.---- along DF 1 (Fig. 3; Table 1), followed by habitat type, substrate (size, water depth, time of sample and water temperature:.. Habitat breadth of the species examined was estimated by the distribution of these species along DF 1-(Fig. 3). The values for Colorado squawfish, fathead minnow and red shiner tended to cluster around the center of the DF and therefore these species were considered to have narrow habitat breadth. In contrast, Age-0 channel catfish and flannelmouth sucker were more evenly dispersed along DF land were considered to have a wider habitat breadth. Calculation of the habitat overlap index showed high spatial overlap between Age-0 Colorado squawfish and fathead minnow (0.8) and red shiner (0.9) (Fig. 3). Overlap is generally (considered to be biologically important when the index value exceeds 0.6 Matthews ;hand Hi11 1980), which is the case between these species. Habitat overlap between ;small Colorado squawfish and small channel catfish (0.5) and flannelmouth sucker .(0.4) was considerably less than observed with the other species. Food Habits and Dietary Overlap Food habits were summarized for two size classes of four species: Colorado squawfish, 22-40 mm and 41-59 mm TL; red shiner 15-34 and 35-69 mm TL; fathead minnow 22-34 and 35-62 mm TL; and channel catfish 19-55 and 85-114 mm TL (Table 2). Smaller Colorado squawfish fed predominantly on aquatic invertebrates and some E fish. Larger Colorado squawfish fed heavily on fish -- mostly red shiner. Both size classes of red shiner and channel catfish fed heavily upon aquatic insect 1r larvae, but consumed a wider variety of taxa than did Colorado squawfish. Both size groups of the fathead minnow fed heavily upon minute plant remains (Seston), ,primarily diatoms, green algae and blue-green algae. None of the introduced fish 'species contained fish remains. U A comparison of the diet overlap indexes shows high overlap for the smaller 1size group of Colorado squawfish with small channel catfish (15-55 mm TL) and l1 , with both size classes of red shiner (Fig. 4). Overlap is reduced between these species and larger Colorado squawfish. Neither size class of Colorado squawfish overlaps with fathead minnow to any extent. The decrease in dietary overlap is presumed to be related to the increasing consumption of fish by Colorado squawfish as they increase in length and become more piscivorous (Fig. 5). DISCUSSION There was no clear partitioning of space between the small fish species examined in this study as has been reported by investigators working in lakes (Werner et al. 1977) and more structured streams (Baker and Ross 1981). Cover and position in the water column tended to be important variables separating fish species spatially in those studies, but position in the water column could not ?be measured in this study and cover (except for turbidity or water depth) tends to be absent in the study areas we examined. :Matthews and Hill (1980) found 48 R