NEILSON ET AL.: DIMENSIONS OF SALMONID OTOLITH NUCLEI 



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Figure 4. — Deadman River steelhead trout sagittal primordia before fusion (right, 214 degree-days) and after fusion (left, 331 



degree-days). Bar = 10 /xm. 



We determined the effect of nucleus size varia- 

 tion on otolith size by examining correlations be- 

 tween nucleus area and otolith area at several 

 stages of development of steelhead trout and O. 

 tshawytscha of similar size. We chose to report 

 nucleus area in this case, as it reflects nucleus 

 dimension more precisely than one-dimensional 

 measurements such as nucleus length. While 

 nucleus area and length are significantly corre- 

 lated (P < 0.001), nucleus length accounted for 

 only 47 and 52% of the variability in nucleus area 

 in steelhead trout and O. tshawytscha, respec- 

 tively. The best correlations between nucleus area 

 and subsequent otolith area were noted in rela- 

 tively small otoliths of recently hatched alevins. 

 The greatest degree of variability in otolith 

 area occurred up to 15 d after nucleus formation 

 (Table 1). 



Table l. — Coefficients of variability in otolith area at several 

 stages of development, and coefficients of determination for re- 

 gressions of otolith area at several stages of development. N = 

 15 for both steelhead trout and Oncorhynchus tshawytscha. The 

 steelhead trout were 29-30 mm FL, and O. tshawytscha 30-31 

 mm. Trout were reared at 9.5°C and O. tshawytscha at 6°C. 



" = P sO.01. 

 NS = not significant (P > 0.05). 



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