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Fishery Bulletin 91(1). 1993 



lized sooner at low temperatures, but activity of me- 

 dium fish stabilized later at low temperatures. 



Transfers The general response to a 5° C change was 

 an almost immediate shift in activity in the expected 

 direction (upward transfers produced higher activity, 

 downward transfers produced lower activity) to a level 

 greater than the stabilized value attained after about 

 2.5 h (Fig. 2). In upward transfers, elevated activity 

 persisted for 1-2 h, rising during the first 20-30 min 

 from an implicit value of zero just prior to transfer. 

 The response of fish to downward transfer was an 

 almost immediate drop in activity to minimum values 

 followed quickly by increasing activity (Fig. 2). 



Activity of small fish after upward transfer was 

 significantly different from that of low controls (Table 

 1). Differences were concentrated in the early part of 

 the experiments, when transferred fish were more ac- 

 tive than controls in six of the first seven time-periods 

 (Fig. 2). Medium and large fish did not show overall 

 differences between upward transfers and controls 



(Table 11, and there were few significant differences at 

 individual time-periods. 



Downward transfer also had a significant influence 

 on activity in comparisons with high controls, but only 

 for small and medium fish (Table 1). Transferred fish 

 were less active than controls in the first six time- 

 periods for small fish and in five of the first nine time- 

 periods for medium fish (Fig. 2). Large fish did not 

 show an overall difference between downward trans- 

 fer and control treatments, and only a single differ- 

 ence for individual time-periods was statistically sig- 

 nificant (Fig. 2). 



Pause frequency 



The number of pauses during the 5-min observation 

 periods generally decreased as fish grew (Fig. 3). Small 

 control fish (temperatures and times combined) paused 

 an average of 24.6 (±11.5) times in 5 min; medium and 

 large fish paused 10.8 (±6.9) and 9.5 (±7.3) times, re- 

 spectively. All main effects (size-class, temperature 



