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FISHERY BULLETIN; VOL. 83, NO. 1 



variance and the Student-Newman-Keuls test, P 

 > 0.05). 



Oncorhynchus tshawytscha transferred from a 

 4°C diel temperature regime (24-h period) to a 

 regime with a 12-h period and similar amplitude 

 produced an average of 1.56 increments/24 h. The 

 slope of the regression of mean increment count on 

 experiment day differed significantly from unity 

 (P < 0.01). An example of an otolith from a fish 

 exposed to the 12-h period, cyclic temperature re- 

 gime is shown in Figure 3 and illustrates the nar- 

 rower increments associated with the 12-h cycle. 



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Otolith growth increments were formed at the 

 rate of one every 24 h in fish fed once per day. No 

 significant departures were noted (^-tests, n ^ 20, 

 P > 0.05). Fish which received 2 feedings/24 h or 1 

 feeding and a 10-min bout of activity deposited 

 significantly >1 increment/24 h (i-tests, P < 0.01). 

 Arithmetic mean regressions of increment counts 

 on experiment day for the latter treatments are 

 given below: 



Slopes of regressions in groups of fish producing 

 >1 increment/d did not differ significantly from 

 each other (analysis of covariance, P > 0.10). 



The distributions of increment widths in fed 

 groups of fish are presented in Figure 4. A sum- 

 mary of the comparisons of increment width data 

 among treatments is provided in Figure 5. One- 

 way analysis of variance and the Student- 

 Newman-Keuls test indicated that mean incre- 

 ment widths in otoliths offish receiving a ration of 

 8% B.W./24 h in one feeding differed significantly 

 between groups (P < 0.05). Mean increment 

 widths in otoliths of fish receiving a ration of 4% 

 B.W./24 h in one feeding did not differ signifi- 

 cantly in fish receiving the ration either during 

 the cool or warm portion of the diel temperature 

 cycle (Student-Newman-Keuls test, P > 0.05). 

 However, fish receiving 4% B.W./24 h under con- 

 stant water temperature produced growth incre- 

 ments whose mean width was significantly less 

 than those of fish held in the diel water- 



94 



