NEILSON ET AL.: DIMENSIONS OF SALMONID OTOLITH NUCLEI 



micrometer along the longest axis through the 

 nuclear zone. The area of the otolith nucleus was 

 measured from photographic enlargements with a 

 polar planimeter. Increment widths were mea- 

 sured with a vernier caliper from photographic 

 enlargements (final magnification 9700 x). The 

 frequency of increment formation was determined 

 from slopes of regressions of increment counts 

 from otoliths offish of known age. 



Nucleus measurements and primordia counts 

 are only reported for otoliths removed from the 

 fishes' left side as nucleus lengths were signifi- 

 cantly greater in left-side than right-side sagittae, 

 albeit at a low level of significance {P < 0.10, 

 Wilcoxon Paired Sample Test). 



During the course of this study, otoliths from 

 257 rainbow trout, 187 steelhead trout, and 50 

 O. tshawytscha were examined. 



RESULTS 



To examine the hypothesis that egg size (a func- 

 tion of female fork length) influences otolith 

 nucleus length in progeny, we examined the rela- 

 tionship of female fork length to egg dry weight 

 and nucleus length in S. gairdneri. The dry weight 

 of steelhead and rainbow trout eggs was positively 

 correlated with the size of the female from which 

 the eggs originated (r^ = 0.54, P < 0.001, Fig. 2). 

 The slope of the geometric mean regression shown 



0.042 -1 



0.040- 



0.038- 



0.036 



D) 



0.034- 



s: 



^ 0.032 

 >. 



d 



Q) 0.030 



o> 



LlJ 



c 



g 0.028 



0.026- 



0.024 



0.022- 



0,020 



y=0.2204x10-^(x)+0.0198 



200 



300 



400 



500 



600 



700 



800 



900 



Fork Length (mm) 



Figure 2. — Geometric mean regression of mean unfertilized egg dry weight on fork length of 

 female Salmo gairdneri from which eggs were obtained. Each point is the mean of 20 eggs from each 

 female. Fish in the 300-400 mm size interval were rainbow trout from Pennask Lake, those 500-600 

 mm were rainbow trout from Mission Creek, and those >700 mm were Deadman or Nicola River 

 steelhead. 



83 



