Kodak Fixer, rinsed for 20 minutes in distilled 

 water, and viewed under transmitted light with a 

 compound microscope at 400 x magnification to 

 determine presence and location of exposed silver 

 grains. Growth increments were enumerated 

 from the time-mark to the otolith margin. In most 

 of the otoliths, a check (or exceptionally dense 

 band) was noted prior to the deposition of the 

 radioactive mark. The location of this check, in 

 terms of numbers of increments from the time- 

 mark, was also determined. 



Oxytetracycline 



A stock solution was prepared using 25 mg 

 OTC (Sigma Chemicals Co.) in 5 mL of physiolog- 

 ical saline. Each fish received a dosage of 0.5 mg 

 OTC or 0.1 mL of stock solution. This approxi- 

 mates the dosage reported by Mugiya and Mura- 

 matsu (1982) for goldfish and Weber and Ridgway 

 (1962) for sockeye salmon smolts. Fish were sacri- 

 ficed 21 days after injection, weighed and mea- 

 sured, and both sagittal otoliths were removed, 

 cleaned, and stored dry in the dark. 



A sagittal section of the right otolith was pre- 

 pared as previously described. Sections were 

 viewed at 160 x magnification, using a compound 

 light microscope equipped with ultraviolet illu- 

 mination. The fluorescent mark was located with 

 an ocular marker. Increments were enumerated 

 from this mark to the outer margins of the otolith 

 using visible light. 



Results and Discussion 

 Calcium-45 



One hundred and three black rockfish were in- 

 jected with the radioisotope, calcium-45; there 

 were no mortalities during the 63-d postinjection 

 sampling period. Over the course of the experi- 

 ment, average fish length increased from 52.5 

 mm (SD = 1.29, N = 4) on day zero to 70.5 mm 

 (SD = 8.23, N = 4) on day 63; average total body 

 weight increased from 2.3 g (SD = 0.13, N = 4) to 

 8.10 g(SD = 2.60, A^ = 4). 



LSC demonstrated that calcium-45 was taken 

 up and retained in the sagittal otoliths of all fish. 

 Incorporation of calcium-45 into the otolith oc- 

 curred as early as 1 hour following injection, 

 which was the initial sampling interval; mean 

 activity at this time was 1,377 (SE = 329) DPM/ 

 mg otolith (Fig. 1). Similar activity values and 

 uptake patterns of calcium-45, up to 72 hours 



0.00 10.00 20 00 30.00 40.00 50.00 60.00 70,00 



DAYS AFTER INJECTION 



Figure 1. — Accumulation and retention of ^sCa in the otolith of 

 black rockfish. Mean activity and 1 SE are indicated. N = 2 to 4 

 fish per time interval. 



postinjection, were observed in the otoliths of 

 rainbow trout, although times of maximum incor- 

 poration and retention were not assessed over 

 longer periods (Mugiya 1974). Radioactivity in 

 the rockfish otoliths increased sharply for the 

 first 15 days (up to an average of 10,279 DPM/mg, 

 SE = 581), followed by a gradual increase to an 

 apparent asymptote (Fig. 1). The rapid uptake 

 and retention of calcium-45 in liver, muscle, and 

 epidermis of .S. melanops, and the gradual elimi- 

 nation of the isotope from these tissues (Yok- 

 lavich and Boehlert unpubl. data), could con- 

 tribute to the increase in otolith activity over 

 time; presumably, calcium-45 is transported from 

 these tissues to the otolith via the blood (Mugiya 

 1974). The lack of decrease in activity in the 

 otolith substantiates the findings of Ichii and 

 Mugiya (1983) and Campana (1983b), which sug- 

 gest that calcium deposited in otoliths of goldfish 

 and stressed coho salmon, respectively, remains 

 immobilized and is not resorbed. Although no 

 data were presented, it had been suggested ear- 

 lier by Pannella (1980) that resorption of calcium 

 occurs in the otoliths of some tropical fish species, 

 possibly invalidating ages based on increment 

 counts. Our data show no evidence of resorption, 

 lending support to the usefulness of increment 

 counts in reliably estimating age. 



Scattered exposed silver grains were evident 

 along the interface of otolith section and mount- 

 ing resin in the autoradiographs of otoliths from 

 the earliest sampling periods (1 hour to 1 day), 

 although positive association of the grains with a 



828 



