JONES and BROTHERS: AGING TECHNIQUE FOR STRIPED BASS LARVAE 



BEI, respectively. Light microscope-counted incre- 

 ments of intermittently starved larvae underesti- 

 mated age by 4 days (Table 4). The standard error 

 of the mean was 4.9 days. For this sample, both 

 SEM techniques also gave more accurate age 

 estimates. SEI underestimated age by 3 days (SE 



= 2.4 days), and BEI underestimated age by 2 days 

 (SE = 2.6 days). 



The comparison between SEI and BEI showed no 

 significant difference in accuracy (Tables 3, 4). 

 Figures 2A and 2B illustrate the increment struc- 

 ture observed with these two methods of SEM. BEI 



Figure 2.— Comparison of otoliths of larval striped bass using two scanning electron micro- 

 scope (SEM), techniques. A) Normal secondary emission (SEI) photomicrograph of an otolith 

 of a larva starved for the first 15 days posthatch then fed ad libitum until sacrificed. Incre- 

 ment width during starvation is approximately 5 /.im. B) Backscattered emission (BEI) photo- 

 micrograph for a comparable otolith to A above. Legends in the micrographs indicate 1) length 

 of scale bars in p^m, 2) accelerating voltage KV, 3) mm working distance, 4) coded photo number. 



175 



