JONES and BROTHERS: AGING TECHNIQUE FOR STRIPED BASS LARVAE 



grit and final polishing was done with 0.25 /um dia- 

 mond paste. These otoliths were etched with 0.02N 

 HCl, then mounted on SEM stubs and sputter 

 coated with gold/palladium. 



Three light microscopes were used: a Zeiss, a 

 Leitz, and an Olympus. The latter two were 

 equipped with video viewing systems and polarized 

 light sources. Readings were done with brightfield 

 illumination at 400, 540, and 1,000 power. Video in- 

 creased magnification to a maximum of 2700 x . The 

 maximum resolution for the light microscopes was 

 0.5-1.0 nm. The SEM employed was a JOEL (JSM 

 200) equipped with both secondary electron image 

 (SEI) and backscattered electron image (BE I) 

 collectors. 



For light microscopy, slides were chosen at ran- 

 dom and read double blind (age of the larvae and 

 condition were unknown). Readings were done three 

 times for each slide. Each slide was counted only 

 once during each session so that replicate counts did 

 not immediately follow each other. Thirteen of the 

 twenty-four samples from conditions 3 and 4 were 

 used for SEM analysis. For SEM examinations. 



counts were blind (ages of the larvae were un- 

 known); condition, however, was selected by the in- 

 vestigators to check the accuracy of the light micro- 

 scope counts for conditions 3 and 4. 



RESULTS 



Light Microscopy 



The relationship between the number of otolith 

 increments and age, in days, for the four experi- 

 mental conditions is shown in Figure 1. Fully fed 

 larvae {n = 63), condition 1, had a regression slope 

 of 0.98 increments/day, and the smallest standard 

 error (Table 2). Its confidence interval included 1 

 increment/day. Beyond 68 days of age sagittae 

 became very difficult to read. Continuous counting 

 paths or an appropriate series of transects were dif- 

 ficult to find because the sagitta changes shape and 

 develops new centers of deposition around the 

 periphery of the otolith. This resulted in underesti- 

 mates of true age (Table 2) for larvae older than 2 

 months of age. 



INCREMENT COUNTS VERSUS KNOWN AGE 



10 20 30 40 50 60 70 80 90 100 



AGE (days) 



Figure 1.— Relationship between otolith increment count in larval striped bass and true age 

 for four feeding regimes, light microscope observations. 



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