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Fishery Bulletin 89(2). 1991 



1000 '600 2200 0400 



Time of day (hours) 



Figure 3 



Diel variations in serum calcium concentra- 

 tions (upper graph) and in vitro calcium 

 deposition on otoliths (lower graph) in On- 

 corhynchus mykiss. Each plotted value 

 represents mean ± SE of 7 fish for serum 

 calcium and of 12-14 otoliths. *P<0.05 for 

 1600 hours; **P< 0.001 for 1600 hours. 



Table 2 



Diel variations in muscle RNA and DNA concentrations 

 (mg/g) in rainbow trout Oncorhynchus mykiss. 



Time of day (h) 



RNA 



DNA 



1000 

 1600 

 2200 

 0400 



1.26 ±0.08 

 1.30 ± 0.08 

 0.66 ± 0.04* 

 0.80 ± 0.04 



0.66 ± 0.04 

 0.72 ± 0.02 

 0.76 ± 0.06 

 0.68 ± 0.04 



Values are mean ± SE of 7 fish. 

 *P<0.01 for 1600 hours. 



RNA-DNA ratios ranged from 1.91 to 2.73, with a 

 mean value of 2.44 in the control group. One day's star- 

 vation had no effect on the ratio (Fig. 2). The first 

 significant (P<0.05) effect occurred on day 2 after star- 

 vation, followed by further decrease to approximately 

 half of the control on day 3. This reduced level appar- 

 ently remained essentially unchanged through day 5. 

 In contrast to the response observed for otoliths, re- 

 feeding had no effect on the recovery in RNA-DNA 

 ratios the next day (Fig. 2). Ratios increased gradual- 

 ly with feeding and recovered to the control level on 

 day 4 after refeeding. 



Diel variation 



Serum calcium concentrations varied dielly by approx- 

 imately 4%, and this variation was statistically signif- 

 icant at P = 0.05 (Fig. 3). Calcium concentrations were 

 high during the daytime, but a nadir occurred at 2200 

 hours. 



The profile of diel variations in calcium deposition 

 on otoliths was essentially the same as that of serum 

 calcium concentrations (Fig. 3). The high rate of cal- 

 cium deposition at 1600 hours rapidly decreased by 

 70% (P< 0.001) to a nadir at 2200 hours, followed by 

 an increase toward 0400 hours. 



Diel variations in muscle RNA and DNA concentra- 

 tions and their ratios are presented in Table 2 and 

 Figure 4, respectively. Diel variations were significant 

 in RNA concentrations and RNA-DNA ratios. The pro- 

 file of variations in the ratios was similar to that of 

 calcium deposition on otoliths: high ratios during the 

 daytime were followed by a steep decrease between 

 1600 and 2200 hours. The lowest ratio occurred at 2200 

 hours, and this ratio was highly significant (P<0.001) 

 compared with the ratio at 1600 hours. Differences 

 between 1000 and 1600 hours were not statistically 

 significant in either otolith or muscle, showing that the 

 criterion of similar growth profiles was fulfilled. 



A comparison of variations in calcium deposition on 

 otoliths and RNA-DNA ratios in muscle showed posi- 

 tive relationships through several days after starvation 

 and during the diel experiment. However, uncoupling 

 was found in the recovery processes with refeeding: 

 calcium deposition on otoliths transiently recovered on 

 day 1 after refeeding, while RNA-DNA ratios did not 

 (compare Figures 1 and 2). 



