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that fish were caught randomly through the night and that the stomach <br />contents were in all stages of digestion. We also assumed that some fish <br />regurgitated stomach contents after capture in the nets. In spite of <br />these limitations, nets were the most practical means of sampling <br />fish in Flaming Gorge Reservoir. <br />Stomach samples collected were preserved in a 10 percent solution <br />of formalin and were analyzed individually during the period 1963 to <br />1967 and collectively by size groups - as described by Borgeson (1966) <br />- from 1967 through 1969. Samples included eight size groupings of <br />fish: 200 mm or less, 201-250, 251-300, 301-350, 351-400, 401-450, <br />451-500, and 501-550 mm. <br />The contents of the complete digestive tract were analyzed from <br />1963 through 1966. The contents of the digestive tract from the <br />esophagus to the pylorus were analysed from 1967 through 1969. The <br />contents of the hindgut were not studied after 1966 because of the large <br />percentage of unidentifiable material. <br />All summarization and statistical analysis of the data were accomp- <br />lished by computer. Significant differences in the "t" distribution <br />(two-tailed-test) are reported at the 99 and 95 percent levels of <br />significance. <br />RESULTS <br />A total of 11413 stomachs were analyzed, 1,343 from rainbow trout, <br />64 from brown trout and six from sutthroat trout. Empty stomachs <br />were excluded. In pooled data fish, zooplankton, diptera, hymenoptera, <br />and organic debris generally comprised more than 15.0 percent by <br />volume of the stomach contents (Table 1). We considered food items <br />contributing, volumetrically, 15.0 percent or more to be major food <br />items. Of the five major foods, zooplankton consistently made up the <br />largest volume (Table 2, Figures 2 and 3). <br />Rainbow trout of all sizes and brown trout up to 401 mm (15.8 <br />inches) included substantial amounts of zooplankton in their diet. <br />Zooplankton may be preferred or may be more available than other <br />types of food. Swift (1970), Williams (1954), McAfee (1966), and <br />Weidlein (1971) also found the primary food of rainbow in impound- <br />ments to be zooplankton. <br />Zooplankton were more common in the stomachs of fish collected <br />from the open and inflow areas (Table 3). Varley (1967) stated that <br />zooplankton production was greatest in the area from Sheep Creek to <br />Buckboard (Figure 1). These data suggest that zooplakton abundance <br />and the utilization of zooplankton by trout were positively correlated. <br />5