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11 <br />parental effects, but is otherwise unexplained. <br />Charts from Ryan thermographs placed in the Yampa River and in the <br />Green River above and below the confluence of the Yampa were obtained from <br />the U.S. Fish and Wildlife Service's, Vernal, Utah, office. Daily <br />temperature fluctuation at each station was about 2 C, but temperature <br />varied considerably among stations (Table 3). Subtraction of the Green <br />River temperature above the confluence from the Yampa River temperature <br />showed that the maximum temperature differential was about 6-7 C during the <br />time that fish larvae were entering the Green. The difference was still 4-5 <br />C at the site of the downstream recorder. <br /> <br />DISCUSSION <br />The marked behavioral changes followed by high initial mortality and <br />finally by significantly higher total mortality of fish shocked with a 15 C <br />temperature decrease in 5 minutes showed that such temperature decreases <br />are harmful to 14-day-old squawfish. A nomograph summarizing data from <br />other studies can be used to show that these results agree with other data, <br />and to predict more closely a temperature shock where mortality might begin <br />(Figure 2). The 15 C decrease which caused 10-40% higher mortality than <br />controls is in the "lethal" portion of the nomograph, whereas the 10 C <br />decrease which caused no greater mortalities than controls, lies <br />comfortably in the "safe" portion. The graph indicates that for fish <br />acclimated to 22 C, as they were in this study, deaths might begin to occur <br />with about a 13.5 C decrease. <br />These findings agree with most of the literature that shows that some <br />larval fish can tolerate 8-15 C temperature decreases (Table 4).