546 



Fishery Bulletin 103(3) 



Daily increments 



8.5 12.3 

 Otolith radius (urn) 



Figure 1 



Diagram describing hatching check deposition as well as initiation of daily otolith 

 increment formation in the sagittae and lapilli of spot [Leiostomus xanthurus) (A). Pho- 

 tographs of the otoliths of a 12-day-old larva: lapilli with six increments IB) and sagitta 

 with 12 increments (C). Scale bar = 8 iim. H = hatching check; FI = first increment. 



the core towards the otolith edge. In both sagittal prepa- 

 rations, increment counts could not easily be made along 

 one radius owing to changes in the growth trajectories 

 (Fig. 2A) and to discontinuities in increment formation 

 (Fig. 2B). However, increment counts could be made along 

 one radius in the lapillus (Fig. 2C) — an advantage that 

 may facilitate measurements of otolith increment widths 

 in future studies. 



A hatching check was identified in the sagittae of 

 34-day-old larvae and 54-day-old juveniles at a location 

 approximately 8.4 pm radius from the core (Table 1). 

 In addition to the hatching check, another well-defined 

 increment was observed in the core area of the sagittal 

 otoliths (Fig. 3A), and this second check was likely re- 

 lated to a dietary switch to exogenous feeding. In most 

 fish the second check was separated from the hatching 

 check by an average of 5.2 increments (t? = 49, SD = 0.59). 

 However, in some fish (n = 9), no increments were visible 



between the hatching check and the other well-defined 

 increment. This observation indicates that there may be 

 problems resolving increments near the core, similar to 

 the results presented above regarding the timing of first 

 increment formation. Owing to the apparent problems 

 discerning increments near the core, the second check 

 was used as a starting point for increment counts. Us- 

 ing the second check as a starting point influenced ac- 

 curacy but provided a clear starting point for increment 

 counts in all sagittal otolith preparations. 



In the lapilli, increment deposition began from a pro- 

 nounced check visible at ca. 12.3 urn radius from the 

 otolith core (Fig. 3B). This check was found at the same 

 distance from the core in lapilli of 12- and 27-day-old 

 larvae in the experiment on first-increment formation 

 (Table 1). Beginning increment counts from this check 

 would underestimate age by 6-7 days owing to the tim- 

 ing of first-increment formation on the lapilli. 



