NEILSON and GEEN: CfflNOOK SALMON OTOLITH INCREMENT FORMATION 



3.5n 



E 3- 



•g 



5 2.5- 



c 



(0 

 0) 



2- 



c 

 



E 



b 



c 



ii.5- 



o 

 O 



1- 



0.5- 



^- 



'^o  "o 

  o 







I 

 10 



~^ 



— I — 

 30 



— I — 

 40 



Experiment Day 



50 



Figure 6. — Mean otolith increment widths (0) for Oncorhyn- 

 chus tshawytscha fry from the 2 x 4% experimental feeding 

 regime over days 1-40. Prior to day 1, fish were fed once every 24 

 h. Also shown are mean increment widths (  ) offish from the 8% 

 (constant) feeding regime, where fish received one feeding only 

 every 24 h. 



treatment did not significantly differ from zero (P 

 > 0.10), whereas the former did (f-test, P < 0.01). 



Starved fry continued to produce one otolith in- 

 crement every 24 h. However, the growth incre- 

 ments were faint when observed with a transmit- 

 ted light microscope. That portion of otolith 

 growth formed under starvation conditions was 

 more transparent than the portion of otolith 

 growth produced when fish were fed. Growth in- 

 crement diel periodicity was also more pronounced 

 during the portion of otolith growth corresponding 

 to that period when fish were fed (Fig. 7). 



To confirm that increment widths were propor- 

 tional to fish growth, we plotted instantaneous 

 growth in dry weight against average increment 

 width for all treatments except the starved group 

 (Fig. 8). The coefficient of determination (r^) as- 

 sociated with those treatments in which fish 

 formed 1 growth increment/24 h was 0.735 and the 

 slope of the regression was significantly different 

 from zero (P < 0.01). Note that points associated 

 with treatments in which fish formed more than 1 

 increment/24 h lie considerably above the regres- 

 sion. The regression of these data differs signifi- 



Fed 1x/24h 



% 



SOyum 



Figure 7. — Example of otolith microstructure from a starved Oncorhynchus tshawytscha salmon fry when viewed with transmitted 

 light microscopy. The relatively transparent region near the otolith periphery corresponds to the starvation period. 



97 



