Thompson et a\ Age distribution and growth of Senola dumen/i 



365 



Figure 1 



Scanning electron micrograph of a sagitta (lateral view) (A), lapillus (B), and 

 asteriscus (C) from a 42.7-cm greater amberjack from the north-central Gulf of Mexico. 



where FL^^ = fork length (cm); and 

 SW = sagittal weight (mg). 



Although internal annuluslike features 

 were visible in whole otoliths, they were 

 not sufficiently translucent to permit con- 

 sistent enumeration. Readability was not 

 improved by immersing sagittae in either 

 glycerin or clove oil for up to one year. 

 Surface grooves and ridges were promi- 

 nent on the lateral side of sagittae from 

 young fish but became compressed and 

 indistinguishable in older specimens ow- 

 ing to an over-burden of calcium carbon- 

 ate; a similar observation was reported for 

 marlin (Wilson et al., 1991). External 

 ridges were closely associated with inter- 

 nal microstructure that we interpreted as 

 annuli. Although a first and second annu- 

 lus was visible in whole sagittae, we con- 

 cluded that annuli could not be enumer- 

 ated from whole otoliths for most fish, par- 

 ticularly larger specimens. 



Microstructural growth features were readily vis- 

 ible in most sectioned sagittae; however, the only 

 consistent annuluslike features were regions where 



growth bands converged on the lateral side of the 

 otolith section. These "convergence zones" were in- 

 ternal to the lateral surface of the antirostrum, where 

 numerous growth features (increments) converged 



