FISHERY BULLETIN: VOL. 85, NO. 3 



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 Time of day (hours) 



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FiGURK 3.— Diurnal variations in the in vitro uptake of ■'■"'Ca (•) 

 and ^iH-glutamic acid (J) by otoliths in rainbow trout. Each 

 plotted value represents mean ± SE of 8-10 samples. Dark 

 horizontal bar indicates nocturnal and twilight peri- 

 ods. *P < 0.02 for 2200 h; **P < 0.05 for 1600 h. 



variation with a single peak at 1600 h when ma- 

 trix deposition on the otoliths was lowest (Fig. 4). 

 Note that the active biosynthesis of matrix 

 proteins in the saccular tissue is not necessarily 

 followed by their instantaneous deposition on the 

 otoliths, suggesting the presence of cyclic secre- 

 tion activity in the cells of the sacculus. The rate 

 of calcium uptake by the saccular tissue did not 

 vary much throughout a 24-h period (Fig. 4). 



Ratios of counts of '^■^Ca and -^H-glutamic acid in 

 the respective otoliths magnified the antiphasic 

 relationship between '^^Ca and -^H uptake (Fig. 5). 

 Significant variation (P < 0.01 ) between the peak 

 (1600 h) and the nadir (2200 h) demonstrates the 

 much greater deposition of calcium relative to 

 glutamic acid during the daytime, which suggests 

 that in December the accretion zone forms during 

 the daytime with its peak at dusk. 



DISCUSSION 



Although previous studies (Mugiya et al. 1981; 

 Mugiya 1984) showed that otoliths grew by the 



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1000 1600 2200 0400 



Time of day (hours) 



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Figure 4.— Diurnal variations m the in vitro uptake of ■'■''Ca (•) 

 and 'SH-glutamic acid CJi of saccular tissue in rainbow 

 trout. Each plotted value represents mean ± SE of 8-10 sam- 

 ples. *P < 0.02 for 1000 h. 



diurnal deposition of calcium, it remained to be 

 determined whether matrix deposition on the 

 otoliths was diurnal or not. Histochemically, 

 otolith matrix consists of various kinds of sub- 

 stances such as proteins, acid mucopolysaccha- 

 rides, PAS-positive materials, and lipids (Mugiya 

 1968). Of these, proteins are the most dominant 

 component and are characterized by a high con- 

 tent of acidic amino acids (Degens et al. 1969). In 

 the present study the diurnal deposition of otolith 

 matrix was evident when examined in terms of 

 the incorporation of glutamic acid into otoliths, 

 showing a single peak at night. Interestingly, cal- 

 cium deposition on the same otoliths proceeded 

 most actively at dusk, followed by minimum de- 

 position at night. Thus, it is concluded, in rain- 

 bow trout kept under natural photoperiod, the 

 pace of otolith calcification is almost antiphasal 

 to the pace of matrix deposition on the otoliths. 

 The present results, where both calcium and 



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