396 



Fishery Bulletin 90(2). 1992 



Figure 2 



Urohyal bone oi Lutjanus vittus with one check (129 mmFL) and three checks (242mmFL). 

 measurement. 



A-B taken as hne of 



Age determination 



A preliminary examination of the sagittal otoliths, uro- 

 hyals, scales, and vertebrae from 60 L. vittus indicated 

 that checks were more clearly defined in otoliths and 

 urohyals than in other hard parts. Due to their thick- 

 ness and opacity, otoliths in older fish required section- 

 ing because inner checks were obscured. As urohyals 

 required little preparation before reading, they were 

 chosen as the primary ageing structure; their only 

 disadvantage being that checks in older fish were 

 represented by a cluster of bands, so that determining 

 the point at which the check was formed was somewhat 

 subjective. Otoliths were referred to only when inter- 

 pretation of urohyals was difficult. Urohyals were 

 frozen and the flesh later removed by dipping in boil- 

 ing water for 5 minutes, scrubbing, rinsing, and air dry- 

 ing before long-term storage. 



Urohyals were examined dry on a black surface 

 under incident light using a dissecting microscope. 

 Checks under this lighting appeared as dark (hyaline) 

 bands (Fig. 2). The distance from the origin to each 

 check and the outer margin of the urohyal was mea- 

 sured along the axis indicated in Figure 2. The period- 

 icity of check formation was determined from analysis 

 of the temporal pattern of marginal increment devel- 

 opment (distance from the outermost check to the 

 outer margin of the urohyal) calculated as the index 

 of completion (C) using the formula of Tanaka et al. 

 (1981): 



WJW, 



n-l. 



(1) 



where Wn = marginal increment, and Wn_i = pre- 

 vious complete increment. Analysis of variance was 



