COLBY ET AL.: PRESSURE SENSITIVITY OF ATLANTIC HERRINC 



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Figure 3.— Moving averages of the percentage of correct ver- 

 tical movements for the three developmental stages of herring 

 in the first experiment. Data for control and preexposed her- 

 ring are not plotted separately. 



change were too long and that the test series as a 

 whole was too protracted as well. The fixed na- 

 ture of the pressure series, while reducing the 

 chance that larvae would be overstimulated if 

 initially exposed to higher pressure changes, 

 confounded possible differences in response to 

 different pressure changes with habituation to 

 the stimulus or possible learning effects. A sec- 

 ond series of experiments was designed there- 

 fore to reduce or eliminate some of these prob- 

 lems. 



EXPERIMENT II 



Design 



The major features of the second design were: 



Table 3.— Analysis of variance of the number of 

 compensatory responses of herring in the second 

 experiment and table of means: I = bulla absent, II = 

 bulla liquid filled, III = bulla gas filled. 



Source 



df Mean square 



Developmental stage 2 62.9394 5.86" 



I versus II 1 4091 030 



I and II versus III 1 125.4697 1168" 



Experimental error 30 10.7394 



Average number of compensatory responses per fish: 



Stage I 14 18 (62%) 



Stage II 13.91 (60%) 



Stage III 18.18 (79%) 



"P<001. 



1) a single factor, developmental stage of the 

 bulla system; 2) all herring tested individually; 

 3) an independently randomized test sequence 

 for each fish; 4) each pressure change tested 

 twice; 5) shorter duration of the test series (Fig. 

 lb) (the larvae were subjected to 23 changes of 

 pressure rather than 47 as in the first experi- 

 ment); and 6) experiments started when herring 

 were at the center of the test column. Eleven her- 

 ring of each developmental stage were tested. 



Results 



As in the first experiment, average positions 

 within the test cylinder were calculated for each 

 pressure change. Vertical movements, as indi- 

 cated by successive differences in these averages, 

 were then scored as compensatory, anticompen- 

 satory, or no response. Analysis of variance of the 

 number of scores indicated that herring with 

 gas-filled bullas compensated more frequently 

 than herring having either liquid-filled bullas or 

 no bullas at all (Table 3; Fig. 4). The stage-Ill 

 herring on the average moved vertically to com- 

 pensate 79% of the time compared with 60% and 

 62% for stage-II and stage-I herring, respectively. 

 However, in Figure 4 we show that even several 

 stage-I larvae achieved relatively high scores, 

 suggesting that a different test of the hypothesis 

 might be based upon classifying larvae into two 



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NUMBER OF ANTICOMPENSATORY MOVES 



Figure 4.— Total numbers of compensatory vertical move- 

 ments by individual herring in Experiment II plotted against 

 the number of anticompensatorymoves. (See legend for Fig. 2.) 



571 



