MUGIYA: DIURNAL GROWTH OF RAINBOW TROUT OTOLITHS 



the highly aberrant form was found by inspection 

 after incubation, it was excluded from the data. 



RESULTS 



Serum calcium concentrations varied diurnally 

 by approximately 89f in a single phasic pattern 

 (Fig. 1). The maximum level (5.47 meq/L) oc- 

 curred at dusk (1600 h), followed by a rapid de- 

 crease (P < 0.05) to a nadir (5.04 meq/L) at night 

 (2200 h). The level then gradually increased to- 

 ward the next peak. In contrast, serum sodium 

 concentrations showed a statistically insignifi- 

 cant variation of only 0.67c iP > 0.05; 148.1-149.0 

 meq/L) throughout a 24-h period. 



When otolith-containing sacculi were incu- 

 bated with '^H-glutamic acid, the saccular tissue 

 (without otoliths) was almost saturated with the 

 isotope within the first 30 minutes or hour of in- 

 cubation (Fig. 2). Otoliths also showed a consider- 

 able uptake (about 60'/^ of the total) of the isotope 

 in the first 30 minutes, followed by a gradual 

 increase in radioactivity until 3 hours, when the 

 incubation was terminated. Tritium activities 

 were always 6-8 times higher in the saccular tis- 

 sue than in the respective otolith (Fig. 2). The 



150- 

 il49 

 f 148 



147 



56 

 55 

 5.4 



i 5 3 



5.1 

 5.0 



4.9 



time-related uptake of '^^Ca by these tissue frac- 

 tions has been reported (Mugiya 1984). In that 

 study, the saccular tissue was saturated with 

 '^^Ca within the first hour of incubation, while 

 otoliths showed an almost linear increase in "^^Ca 

 uptake during the first 5 hours at which point the 

 incubation was terminated. 



The uptake of calcium by otoliths varied diur- 

 nally (Fig. 3), and the pattern was quite similar to 

 that of diurnal variations in serum calcium con- 

 centrations (Fig. 1). The rate of calcium uptake 

 was intermediate at 1000 h, peaked at dusk ( 1600 

 h), and then decreased significantly (P < 0.02) by 

 37% to a nadir at night (2200 h). The low rate 

 persisted through the night, increasing slightly 

 at 0400 h. Clearly otolith calcification proceeded 

 more actively during the daytime. The uptake of 

 glutamic acid by the same otoliths also showed a 

 diurnal variation, and its profile was almost an- 

 tiphasic to that of calcium uptake (Fig. 3). The 

 rate of the uptake remained rather low during the 

 daytime with a small nadir at dusk ( 1600 h). Then 

 the rate increased significantly (P < 0.05) to a 

 peak at night (2200 h), followed by a return to the 

 daytime level. Thus the most active deposition of 

 otolith matrix (at least proteins) occurred during 

 the first half of the nighttime period, when cal- 

 cium deposition was at its lowest level. 



The uptake of glumatic acid by the saccular 

 tissue showed significant (P<0.02), diurnal 



X 10 for 

 sacculus 



800 



^ 600 



^ 400 



i 200 







0.5 



Hours in incubation 



1000 1600 2200 0400 



Time of day (hours) 



1000 



Figure 1. — Diurnal variations in serum calcium (•) and 

 sodium fCi concentrations in rainbow trout. Each plotted 

 value represents mean ± SE of 5 or 6 fish. P < 0.05 for 2200 

 h. 



Figure 2. — Time course for the in vitro uptake of ^H-glutamic 

 acid by otoliths (•) and the saccular tissue (O) of isolated sacculi 

 in rainbow trout. The radioactivity of the saccular tissue is 

 expressed as dpm per otolith weight (mg) because the dry 

 weight of the individual saccular tissue was too light to be 

 determined accurately. Each plotted value represents mean 

 ±SE of 8-10 samples. 



397 



