. Bulletin. Natural history; Natural history. August, 1957 Larimore: Life History of the Warmouth 11 All fish were taken with a rowboat fish shocker (Larimore, Durham, & Bennett 1950), fig. 5. Regurgitation of food by the fish was not caused by the shocker as it was used in this study. While the fish'were fresh, their stomachs were removed and Survey. It was found to be convenient and reliable. When items were measured by both methods, the volume determined by one method agreed closely with the volume determined by the other. The sum of vol- umes of the different kinds of food in each. Fig
. Bulletin. Natural history; Natural history. August, 1957 Larimore: Life History of the Warmouth 11 All fish were taken with a rowboat fish shocker (Larimore, Durham, & Bennett 1950), fig. 5. Regurgitation of food by the fish was not caused by the shocker as it was used in this study. While the fish'were fresh, their stomachs were removed and Survey. It was found to be convenient and reliable. When items were measured by both methods, the volume determined by one method agreed closely with the volume determined by the other. The sum of vol- umes of the different kinds of food in each. Fig. 5.—An electric fish shocker being used from a rowboat to collect warmouths in Park Pond. placed in cheesecloth bags; the bags were labeled and placed in formalin. Other parts of the digestive tracts were discarded. In the laboratory, each stomach was first studied as a unit. The contents were removed and their total volume was meas- ured. Then the contents were sorted under a dissecting microscope (magnifi- cation 9 to 48 times) into various taxo- nomic categories, table 5. The number of individual organisms and the volume of each kind of food were determined. Volu- metric measurement was made by one of two methods: large, irregular masses of food were measured by water displacement in a calibrated centrifuge tube; small, compact items were measured by compari- son with cork blocks of known volumes. This second method was devised by the late R. E. Richardson, for several years employed by the Illinois Natural History stomach was checked against the total vol- ume recorded for each stomach when the contents were removed. After data for the sorted food materials had been tabulated, calculations were made that involved (1) the percentage of stomachs in which each kind of food oc- curred {frequency of occurrence), (2) the average number of items of each kind of food in the stomachs containing the food [average number of items), (3) the aver- age of the percentages of volume com
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