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J ? <br />shock can be lethal, and "tempering" fish is recommended when temperature <br />differences exceed 3 C (Meyer et al. 1973). Additionally, sublethal changes in <br />behavior of shocked fish can lead to increased susceptibility to predation by <br />fish and birds (Coutant 1977). Consequently, we conducted laboratory bioassays <br />to determine the effect of cold shock on Colorado squawfish larvae. <br />Squawfish sac fry were shipped from Dexter National Fish Hatchery to Utah <br />State University in early June 1984 and 1985. Larvae were held at 22 C in 20 <br />gallon aquaria and fed brine shrimp ad libitum until selected for use In the <br />bioassay tests. Bioassays were run in one gallon aquaria where light and <br />temperature were controlled (Table 1). We subjected fish to immediate shocks of <br />5, 10, and 15 C (Figure 1) and at rates of 1, 2, and 3 C/hr (Figure 2). <br />We counted the number of dead fish daily, made visual observations of <br />behavior, and measured fish for length attained during the study. A Model I <br />ANOVA was used to determine the effects of shock rate. We report today only the <br />4 <br />preliminary results because the final stages of the research are still underway. <br /> <br />Mor- tality. <br />Mortality was significant only in the case where temperatures decreased 15 <br />C in 5 minutes (Table 2, Figure 3). This trend was evident even though there <br />was an as-yet-unexplained difference in total mortality between the 1984 and <br />1985 experiments. The 10-week-old fish were not effected by conditions of our- <br />w <br />experiment suggesting that the the effect of temperature decreased with fish <br />age. There was a positive relationship between shock rate and percent <br />mortality. Most reports have shown that the faster the rate of temperature <br />a226PrR.crb Page 3