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38 <br />~, <br />~; <br />.~ <br />a <br />~~' <br />S:.. _ '' <br />r;. <br />Confinement may have been a factor in the more erratic behavior of the <br />adult Colorado squawfish, though the gradient trough appeared to .give <br />ample room for the adults to maneuver easily, and the water-depth was <br />more than adequate to completely cover the fish.- Adults acclimated to <br />26 C were the most precise in thermal preference, with a range of in- <br />dividual modes of 24-27 C and a strong pooled mode of 27 C (Table 1, <br />Figure 5). The adults were more difficult to hold in the laboratory, <br />appeared to be more subject to stress, and, except when held at 26 C, <br />did not feed very actively. Stuntz and Magnuson (1976) found that <br />fish losing weight were more variable in their .selected temperatures <br />than were :fish that were growing. A negative energy budget may have <br />been an additional factor in the low thermal responsiveness of adult <br />.squawfish, particularly those acclimated to 14 and 20 C. <br />Juveniles acclimated to 26 C may also have been on a negative en- <br />` ergy budget, particularly during preliminary testing. Although growth <br />i <br />I rate,at 25 C was significantly faster than at 20 C in the- growth,...ex- <br />periment, growth of juveniles held at 20 C during the prelimi-.nary <br />thermal preference testing period:was.much faster;than,.that of fish <br />:held- at either 14 or 26'C. Feeding frequency was increased .from .once <br />or.twice daily 1n the preliminary est to hree ..times. .daily; in the <br />final thermal -preference-test for all lots of>juveniles. Differences <br />in :.acute preferenca between the preliminary and ;final testing of 26 C <br />-acclimated fish tended o substantiate the impression of a negative <br />energy budget in the preliminary test fish. The .;.mean of individual <br />modes for. 26 ~ -acclimated juveniles,-was .21.8 C for the preliminary <br />