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39 <br />test and 23.7 C for-the final test. Stuntz and Magnuson (1976) found <br />that bluegills selected significantly lower temperatures when,-daily <br />ration was less than required for body maintenance. Preferred temper.- <br />. , <br />atures decreased at lower rations enough to cause a decrease in stan- <br />dard metabolism of approximately 5a (Stuntz and Magnuson 1976). <br />Erlich et al. (1979) suggested that selection of colder water during . <br />food deprivation may be a mechanism of energy conservation by poiki- <br />lothermic organisms. <br />Acute preferenda of adult and juvenile squawfish were not signi- <br />ficantly different (Table 2). This result may have been due to inade- <br />quate data for the adult squawfish. Perhaps an even larger trough was <br />needed -for testing adults, but the sensitivity of adults to laboratory <br />conditions could not be avoided,- and probably contributed most to <br />their erratic and variable behavior in the gradient trough. Lower <br />avoidance temperatures were 'not included in the range of temperatures <br />offered- in thegradient. The limited temperature range `resulted in <br />several fish,`especi'ally the adults, remaining at the-coTd end after <br />only a brief -search of the entire gradient. If possibie,''upper"and- <br />a ower avoidance temperatures `should be included in the 'gradient ' to <br />force `t he fish away from-ends of .the .trough. <br />°- Other endemi c fishes of the ..Colorado " River drainage ' have been <br />_ tested for thermal preferences,-and ,had acute and final preferences <br />similar to-those of the squawfish (Bulkley et al. .1981). Final pre- <br />t <br />ferenda of razorback suckers (Xyrauchen texanus) and humpback chubs <br />(Gila cypha) were 23-24 C and 24 C, respectively. Based on their la- <br />