FISHERY BULLETIN: VOL. 83, NO. 1 



(0 



o 



c 

 (1) 



k_ 



o 

 o 



O 



> 



DC 



50n 



8% (warm 



mean width = 3. 77 

 no. of increments=386 

 (099) 



8% (cool) 



8%(constant) 



mean wiclth= 2.78 

 no. of increments =384 

 (0.96) 



mean width = 2.29 

 no. of increments = 36 3 

 (0.94) 



J 



50-, 



25- 



4% (warm) 



mean width = 3.06 

 no. of increments = 37 4 

 (0.98) 



rw 





 50n 



4%(cool) 



I2=i 



mean width = 3.21 

 no of increments = 1 80 

 (0.99) 



4% (constant) 



mean width = 2.23 

 no. of increments = 393 



(1.02) 



i=. 



25- 



0- 



2 X 4% 



mean width = 1 66 

 no of increments=588 

 (1.45) 



J^ 



5 



10 



2x2% 



mean width = 1 .45 

 no of increments = 733 

 (1-76) 



i. 



— r- 

 5 



10 



4% + activity 



mean width = 1 .34 

 no of increments =556 

 (1 50) 



10 



Increment Width i/jjm) 



Figure 4. — Distribution of otolith increment widths under the experimental regimes. Treatments are identified by numbers in the 

 top-left comers of histograms and correspond to treatments listed in Table 1. The average rate of increment formation every 24 h is 

 shown in brackets. 



8%(warm) ». 8%(cool) 



8%(constant)- 



4%(warm 



Figure 5. — Summary of Student-Newman-Keuls or <-test (a = 

 0.05) comparisons of mean increment widths in Oncorhynchus 

 tshawytscha fry held under the various experimental regimes. 

 Arrow heads pointing left or right signify "less than" and 

 "greater than" respectively. 



96 



a 10-min period of enforced activity. The mean 

 increment width associated with the latter treat- 

 ment was significantly less (^-test, P < 0.01). 



Production of the narrower growth increments 

 associated with 2 feedings/24 h or 1 feeding and 

 induced activity did not occur immediately upon 

 commencement of the experimental regimes. A 

 period of transition in otolith microstructure was 

 evident. Figure 6 shows the decrease in increment 

 widths with time in fish previously provided a 

 ration of 8% B.W./24 h in one feeding and then 

 offered the same total ration in 2 feedings/d. For 

 comparison, data on increment widths in fish fed 

 8% B.W./24 h are provided (Fig. 6). The slope of the 

 regression of increment width on date in the latter 



